1. infrequent Unique is alone of its kind; rare is infrequent of its kind; great poems are rare; "Paradise Lost" is unique. To say of a thing that it is rare is simply to affirm that it is now seldom f Synonyms: rare, curious, odd, scarce, unique, extraordinary, peculiar, singular, unparalleled, incomparable, precious, strange, unprecedented, infrequent, remarkable, uncommon, unusual