A unique specimen.

The small gap in a needle, with just enough space for a thread to pass through.

Unique, singular, sui generis.

A unique example.

extreme enthusiasm shown by a person who has recently taken a new task or set of beliefs.

Without any doubt or hesitation at all.

(idiomatic, archaic) The worth of some trifling or insignificant matter; a whit or jot of value.

Adjectival or attributive form of angels dancing on the head of a pin.

(figuratively) The subject of arcane intellectual speculation; used as an example subject of enquiry the pursuit of which is of no value.

Alternative spelling of U.S. of A.