one–off

1 being the one or ones of a class with no other members an actress who commissioned a one-off dress from the designer for the Oscars Synonyms alone, lone, one, one-off, singular, sole, solitary, special, sui generis, uniqueRelated Words single, solo, unaccompanied, unattended; incomparable, inimitable, matchless, peerless, unequaled (or unequalled), unmatched, unparalleled, unrivaled (or unrivalled), unsurpassable, unsurpassed; distinct, distinctive, individual, separate; nonceNear Antonyms divers, manifold, multifarious, myriad; assorted, heterogenous, miscellaneous, mixed, motley, patchwork, promiscuous, varied; popular, prevailing, prevalent, rampant; perennial, recurrent, repeated

2 happening only once the tour is a one-off event to commemorate the band's 20th anniversary Synonyms one-off, one-shotRelated Words nonce; inconstant, infrequent, intermittent, irregular, occasionalNear Antonyms common, commonplace, everyday, familiar, ordinary, routine, ubiquitous, usual; cyclic (or cyclical); around-the-clock, constant, continual, hourly, round-the-clock; accustomed, chronic, confirmed, customary, habitual, inveterate; expected; annual, yearlyAntonyms frequent, periodic, periodical, recurrent, recurring, regular, repeated, steady