That which is unusual is something that varies from the ordinary, the expected or the commonplace: It was an unusual day for summer, damp and chilly, with a biting wind more reminiscent of August than January. Unusual is a neutral word; it can be used to describe something thought of as good or something thought of as bad: a gift expressing her unusual generosity; an act that showed unusual malice. Exceptional , like unusual , describes something that departs from the usual; it, too, can function in either a complimentary or a critical description.

• He treated his employees with exceptional kindness; She showed an exceptional disregard for detail in her work.

Exceptional may suggest excellence or superiority in a way that unusual cannot. If one speaks of a singer’s unusual voice, there is no implicit indication of quality. But a reference to a singer’s exceptional voice would almost certainly be a compliment. Exceptional is applied also to children who are mentally or physically gifted, as well as to those who are retarded to the extent that they require special education and psychological aid.

One says of a thing that it is rare when one wishes to describe it as something that is found or occurs but seldom, whether or not it was once common: rare moments of quiet in the midst of a loud debate; a rare out-of-print book which is the only one remaining out of thousands that were printed. That which is rare may be ordinary, but it is usually exceptional , and the word can be employed to identify something that is for superlative or excellent: a gem of rare beauty and worth; a rare ability for handling personnel problems. While something that is rare is infrequent of its kind, something that is unique is alone of its kind.

• Great poems are rare ; "Paradise Lost" is unique .

Unique was once limited in definition to this sense, but usage has extended its meaning to unusual or rare , often preceded by a qualifier: a unique opportunity; a rather unique situation.

Off-beat is slang and means differing from the usual. It implies a departure from the familiar, the orthodox or the conventional, and so it departure from the familiar, the orthodox or the conventional, and so it is often used to describe something of which the speaker or writer is critical: a really bad novel, full of violence and off-beat sex. Nevertheless, since the unusual , the unorthodox and the unconventional are often the forerunners of popular fashions and trends, off-beat may be complimentary in tone in some contexts: Her boutique specializes in off-beat clothes and has become one of the most talked-about fashion spots in town.