1.  gratuitous(s = adj.all) - without cause; "a gratuitous insult"

2.  gratuitous(s = adj.all) complimentary, costless, free, gratis - costing nothing; "complimentary tickets"; "free admission"

3.  gratuitous(s = adj.all) needless, uncalled-for - unnecessary and unwarranted; "a strikers' tent camp...was burned with needless loss of life"

1.  Given without an equivalent or recompense; conferred without valuable consideration; granted without pay, or without claim or merit; not required by justice. [1913 Webster]
"We mistake the gratuitous blessings of Heaven for the fruits of our own industry." [1913 Webster]

2.  Not called for by the circumstances; without reason, cause, or proof; adopted or asserted without any good ground; as, a gratuitous assumption. [1913 Webster]
"Acts of gratuitous self-humiliation."

gratuitous, adj.
1 given or done free of charge.
2 uncalled for; unwarranted; lacking good reason (a gratuitous insult).

Derivative:
gratuitously adv. gratuitousness n.

Etymology:
L gratuitus spontaneous: cf. fortuitous

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.

N  cheapness, low price, depreciation, bargain, good penny worth, snap, gratuity, free quarters, free seats, free admission, pass, free pass, free warren, give-away, freebee, run of one's teeth, nominal price, peppercorn rent, labor of love, drug in the market, deadhead, cheap, low, low priced, moderate, reasonable, inexpensive, unexpensive, well worth the money, worth the money, magnifique et pas cher, good at the price, cheap at the price, dirt cheap, dog cheap, cheap, cheap as dirt, cheap and nasty, catchpenny, discounted, half-price, depreciated, unsalable, gratuitous, gratis, free, for nothing, costless, expenseless, without charge, not charged, untaxed, scotfree, shotfree, rent-free, free of cost, free of expense, honorary, unbought, unpaid, for a mere song, for a song, at cost, at cost price, at prime cost, at a reduction, a bon marche.

N  intuition, instinct, association, hunch, gut feeling, presentiment, premonition, rule of thumb, superstition, astrology, faith (supposition), sophistry, paralogy, perversion, casuistry, jesuitry, equivocation, evasion, chicane, chicanery, quiddet, quiddity, mystification, special pleading, speciousness, nonsense, word sense, tongue sense, false reasoning, vicious reasoning, circular reasoning, petitio principii, ignoratio elenchi, post hoc ergo propter hoc, non sequitur, ignotum per ignotius, misjudgment, false teaching, sophism, solecism, paralogism, quibble, quirk, elenchus, elench, fallacy, quodlibet, subterfuge, subtlety, quillet, inconsistency, antilogy, a delusion, a mockery, and a snare, claptrap, cant, mere words, lame and impotent conclusion, meshes of sophistry, cobwebs of sophistry, flaw in an argument, weak point, bad case, overrefinement, hairsplitting, intuitive, instinctive, impulsive, independent of reason, anterior to reason, gratuitous, hazarded, unconnected, unreasonable, illogical, false, unsound, invalid, unwarranted, not following, inconsequent, inconsequential, inconsistent, absonous, absonant, unscientific, untenable, inconclusive, incorrect, fallacious, fallible, groundless, unproved, non sequitur, it does not follow, deceptive, sophistical, jesuitical, illusive, illusory, specious, hollow, plausible, ad captandum, evasive, irrelevant, weak, feeble, poor, flimsy, loose, vague, irrational, nonsensical, foolish, frivolous, pettifogging, quibbling, finespun, overrefined, at the end of one's tether, au bout de son latin, intuitively, by intuition, illogically, non constat, that goes for nothing.

N  supposition, assumption, assumed position, postulation, condition, presupposition, hypothesis, blue sky hypothesis, postulate, postulatum, theory, thesis, theorem, data, proposition, position, proposal, presumption, divination, conjecture, guess, guesswork, speculation, rough guess, shot, shot in the dark, conjecturality, surmise, suspicion, sneaking suspicion, estimate, approximation (nearness), inkling, suggestion, hint, intimation, notion, impression, bare supposition, vague supposition, loose supposition, loose suggestion, association of ideas, (analogy), metonym, metonymy, simile (metaphor), conceit, idea, thought, original idea, invention (imagination), supposing, given, mooted, postulatory, assumed, supposititious, suppositive, suppositious, gratuitous, speculative, conjectural, hypothetical, theoretical, academic, supposable, presumptive, putative, suppositional, suggestive, allusive, if, if so be, an, on the supposition, ex hypothesi, in the case, in the event of, quasi, as if, provided, perhaps, for aught one knows.