rainy day(n = noun.time) - a (future) time of financial need; "I am saving for a rainy day"
is a kind of period, period of time, time period

N  adversity, evil, failure, bad luck, ill luck, evil luck, adverse luck, hard fortune, hard hap, hard luck, hard lot, frowns of fortune, evil dispensation, evil star, evil genius, vicissitudes of life, ups and downs of life, broken fortunes, hard case, hard lines, hard life, sea of troubles, peck of troubles, hell upon earth, slough of despond, trouble, hardship, curse, blight, blast, load, pressure, pressure of the times, iron age, evil day, time out of joint, hard times, bad times, sad times, rainy day, cloud, dark cloud, gathering clouds, ill wind, visitation, infliction, affliction, bitter pill, care, trial, the sport of fortune, mishap, mischance, misadventure, misfortune, disaster, calamity, catastrophe, accident, casualty, cross, reverse, check, contretemps, rub, backset, comedown, setback, losing game, falling, fall, downfall, ruination, ruinousness, undoing, extremity, ruin, unfortunate, unblest, unhappy, unlucky, improsperous, unprosperous, hoodooed, luckless, hapless, out of luck, in trouble, in a bad way, in an evil plight, under a cloud, clouded, ill off, badly off, in adverse circumstances, poor, behindhand, down in the world, decayed, undone, on the road to ruin, on its last legs, on the wane, in one's utmost need, planet-struck, devoted, born under an evil star, born with a wooden ladle in one's mouth, ill-fated, ill-starred, ill-omened, adverse, untoward, disastrous, calamitous, ruinous, dire, deplorable.

admission day, all day long, all fools' day, all saints' day, all souls' day, american indian day, annunciation day, april fools' day, arbor day, armed forces day, armistice day, ascension day, bastille day, bissextile day, boxing day, break of day, break of the day, by the day, calendar day, call it a day, candlemas day, childermas day, christian holy day, christmas day, citizenship day, civil day, clarence day, clarence shepard day jr., class day, columbus day, commencement day, commonwealth day, day, day after day, day bed, day blindness, day boarder, day book, day by day, day camp, day care, day care center, day game, day in and day out, day in day out, day jessamine, day laborer, day labourer, day lily, day nursery, day of atonement, day of judgement, day of judgment, day of reckoning, day of remembrance, day of rest, day of the month, day of the week, day off, day return, day school, day shift, day watch, decoration day, degree day, discovery day, dominion day, each day, easter day, election day, ember day, empire day, every day, fast day, father's day, feast day, fete day, field day, flag day, forever and a day, future day, gain the day, good day, groundhog day, guy fawkes day, high holy day, holy day, holy day of obligation, holy innocents' day, inauguration day, independence day, innocents' day, jewish holy day, judgement day, judgment day, labor day, lady day, lammas day, last day, leap day, lord's day, lunar day, major fast day, market day, martin luther king day, may day, mean solar day, memorial day, michaelmas day, midsummer day, midsummer's day, minor fast day, mother's day, naked as the day one was born, naked as the day you were born, name day, natal day, new year's day, night and day, order of the day, pan american day, pancake day, patriot's day, patriots' day, pioneers' day, polling day, poppy day, present day, presidents' day, quarter day, rag day, rainy, rainy season, red-letter day, remembrance day, rest day, robert e lee day, rogation day, saint patrick's day, saint valentine's day, saint's day, school day, seize the day, sidereal day, six day war, solar day, speech day, st john's day, st martin's day, st patrick's day, st valentine's day, tag day, term day, texas independence day, thanksgiving day, three kings' day, time of day, transfiguration day, twelfth day, united nations day, unlucky day, v-e day, v-j day, valentine day, valentine's day, veterans day, veterans' day, victoria day, victory day, washing day, wedding day, work day, working day