TITLE: Word for category with unique isomorphisms
QUESTION [6 upvotes]: Is there a standard word to express the fact that a category has at most one isomorphism between any two objects?

REPLY [6 votes]: This is equivalent to being gaunt, a common name for a category with no nontrivial automorphisms. A non-gaunt category certainly has a pair of objects admitting two isomorphism a between them, while if $f,g$ are distinct isomorphisms in any category then $g^{-1}f$ is a non-identity automorphisms, by uniqueness of inverses.