SYN: Timely, seasonable, appropriate, felicitous, suitable, fit, meet, auspicious.
ANT: Inopportune, untimely, unseasonable, infelicitous.
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KEY: Opportunity.
SYN: Occasion, turn, opening, convenience.
ANT: Inopportuneness, unseasonableness, lapse, omission, contretemps.
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KEY: Oppose.
SYN: Withstand, resist, mutch, obstruct, confront, oppugn, bar, hinder, contravene, check, thwart.
ANT: Aid, abet, back, support, advance, expedite.