1.  Well-pleased; glad; apt; wont; fond; inclined. [1913 Webster]
"Men and birds are fain of climbing high." [1913 Webster]
"To a busy man, temptation is fainto climb up together with his business." [1913 Webster]

2.  Satisfied; contented; also, constrained. Shak. [1913 Webster]
"The learned Castalio was fain to make trechers at Basle to keep himself from starving." [1913 Webster]

   With joy; gladly; -- with wold. [1913 Webster]
"He would fain have filled his belly with the husks that the swine did eat." [1913 Webster]
"Fain Would I woo her, yet I dare not." [1913 Webster]

   To be glad ; to wish or desire. [1913 Webster]
"Whoso fair thing does fain to see." [1913 Webster]

fain, adj. & adv. archaic
--predic.adj. (foll. by to + infin.) 1 willing under the circumstances to.
2 left with no alternative but to.
--adv. gladly (esp. would fain).

Etymology:
OE f{aelig}gen f. Gmc

N  willingness, voluntariness, willing mind, heart, disposition, inclination, leaning, animus, frame of mind, humor, mood, vein, bent, penchant, aptitude, docility, docibleness, persuasibleness, persuasibility, pliability, geniality, cordiality, goodwill, alacrity, readiness, earnestness, forwardness, eagerness, asset, compliance, pleasure, gratuitous service, labor of love, volunteer, volunteering, willing, minded, fain, disposed, inclined, favorable, favorably- minded, favorably inclined, favorably disposed, nothing loth, in the vein, in the mood, in the humor, in the mind, ready, forward, earnest, eager, bent upon, predisposed, propense, docile, persuadable, persuasible, suasible, easily persuaded, facile, easy-going, tractable, genial, gracious, cordial, cheering, hearty, content, voluntary, gratuitous, spontaneous, unasked &c (ask), unforced, willingly, fain, freely, as lief, heart and soul, with pleasure, with all one's heart, with open arms, with good will, with right will, de bonne volonte, ex animo, con amore, heart in hand, nothing loth, without reluctance, of one's own accord, graciously, with a good grace, a la bonne heure, by all means, by all manner of means, to one's heart's content, yes, willingness, voluntariness, willing mind, heart, disposition, inclination, leaning, animus, frame of mind, humor, mood, vein, bent, penchant, aptitude, docility, docibleness, persuasibleness, persuasibility, pliability, geniality, cordiality, goodwill, alacrity, readiness, earnestness, forwardness, eagerness, asset, compliance, pleasure, gratuitous service, labor of love, volunteer, volunteering, willing, minded, fain, disposed, inclined, favorable, favorably- minded, favorably inclined, favorably disposed, nothing loth, in the vein, in the mood, in the humor, in the mind, ready, forward, earnest, eager, bent upon, predisposed, propense, docile, persuadable, persuasible, suasible, easily persuaded, facile, easy-going, tractable, genial, gracious, cordial, cheering, hearty, content, voluntary, gratuitous, spontaneous, unasked &c (ask), unforced, willingly, fain, freely, as lief, heart and soul, with pleasure, with all one's heart, with open arms, with good will, with right will, de bonne volonte, ex animo, con amore, heart in hand, nothing loth, without reluctance, of one's own accord, graciously, with a good grace, a la bonne heure, by all means, by all manner of means, to one's heart's content, yes.

N  desire, wish, fancy, fantasy, want, need, exigency, mind, inclination, leaning, bent, animus, partiality, penchant, predilection, propensity, willingness, liking, love, fondness, relish, longing, hankering, inkling, solicitude, anxiety, yearning, coveting, aspiration, ambition, vaulting ambition, eagerness, zeal, ardor, empressement, breathless impatience, overanxiety, impetuosity, appetite, appetition, appetence, appetency, sharp appetite, keenness, hunger, stomach, twist, thirst, thirstiness, drouth, mouthwatering, itch, itching, prurience, cacoethes, cupidity, lust, concupiscence, edge of appetite, edge of hunger, torment of Tantalus, sweet tooth, lickerish tooth, itching palm, longing eye, wistful eye, sheep's eye, greed, voracity, passion, rage, furore, mania, manie, inextinguishable desire, dipsomania, kleptomania, lover, amateur, votary, devotee, aspirant, solicitant, candidate, applicant, supplicant, cormorant, desideratum, want, a consummation devoutly to be wished, attraction, magnet, allurement, fancy, temptation, seduction, fascination, prestige, height of one's ambition, idol, whim, whimsy, whimsey, maggot, hobby, hobby-horse, Fortunatus's cap, wishing cap, wishing stone, wishing well, desirous, desiring, inclined, partial to, fain, wishful, optative, anxious, wistful, curious, at a loss for, sedulous, solicitous, craving, hungry, sharp-set, peckish, ravening, with an empty stomach, esurient, lickerish, thirsty, athirst, parched with thirst, pinched with hunger, famished, dry, drouthy, hungry as a hunter, hungry as a hawk, hungry as a horse, hungry as a church mouse, hungry as a bear, greedy, unsatisfied, unsated, unslaked, unsaturated, eager, avid, keen, burning, fervent, ardent, agog, all agog, breathless, impatient, bent on, intent on, set on, bent upon, intent upon, set upon, mad after, enrage, rabid, dying for, devoured by desire, aspiring, ambitious, vaulting, skyaspiring, high-reaching, desirable, desired, in demand, pleasing, appetizing, appetible, tantalizing, wistfully, fain, Int, would that, would that it were!, O for!, esto perpetual, the wish being father to the thought, sua cuique voluptas, hoc erat in votis, the mouth watering, the fingers itching, aut Caesar aut nullus, Cassius has a lean and hungry look, hungry as the grave, I was born to other things, not what we wish but what we want, such joy ambition finds, the sea hath bounds but deep desire hath none, ubi mel ibi apes, desire, wish, fancy, fantasy, want, need, exigency, mind, inclination, leaning, bent, animus, partiality, penchant, predilection, propensity, willingness, liking, love, fondness, relish, longing, hankering, inkling, solicitude, anxiety, yearning, coveting, aspiration, ambition, vaulting ambition, eagerness, zeal, ardor, empressement, breathless impatience, overanxiety, impetuosity, appetite, appetition, appetence, appetency, sharp appetite, keenness, hunger, stomach, twist, thirst, thirstiness, drouth, mouthwatering, itch, itching, prurience, cacoethes, cupidity, lust, concupiscence, edge of appetite, edge of hunger, torment of Tantalus, sweet tooth, lickerish tooth, itching palm, longing eye, wistful eye, sheep's eye, greed, voracity, passion, rage, furore, mania, manie, inextinguishable desire, dipsomania, kleptomania, lover, amateur, votary, devotee, aspirant, solicitant, candidate, applicant, supplicant, cormorant, desideratum, want, a consummation devoutly to be wished, attraction, magnet, allurement, fancy, temptation, seduction, fascination, prestige, height of one's ambition, idol, whim, whimsy, whimsey, maggot, hobby, hobby-horse, Fortunatus's cap, wishing cap, wishing stone, wishing well, desirous, desiring, inclined, partial to, fain, wishful, optative, anxious, wistful, curious, at a loss for, sedulous, solicitous, craving, hungry, sharp-set, peckish, ravening, with an empty stomach, esurient, lickerish, thirsty, athirst, parched with thirst, pinched with hunger, famished, dry, drouthy, hungry as a hunter, hungry as a hawk, hungry as a horse, hungry as a church mouse, hungry as a bear, greedy, unsatisfied, unsated, unslaked, unsaturated, eager, avid, keen, burning, fervent, ardent, agog, all agog, breathless, impatient, bent on, intent on, set on, bent upon, intent upon, set upon, mad after, enrage, rabid, dying for, devoured by desire, aspiring, ambitious, vaulting, skyaspiring, high-reaching, desirable, desired, in demand, pleasing, appetizing, appetible, tantalizing, wistfully, fain, Int, would that, would that it were!, O for!, esto perpetual, the wish being father to the thought, sua cuique voluptas, hoc erat in votis, the mouth watering, the fingers itching, aut Caesar aut nullus, Cassius has a lean and hungry look, hungry as the grave, I was born to other things, not what we wish but what we want, such joy ambition finds, the sea hath bounds but deep desire hath none, ubi mel ibi apes.