What is a term for a word used only once in Bible?

Answer 1

A word that occurs only once in The Bible is called a hapax legomenon. In respect to ancient Hebrew words, this may result in the word's meaning being unknown. When this happens, translators consult other sources which in most cases supplies an appropriate meaning. Faling this, they can only guess what the word meant, based on the context.

This can occur in the case of both the Old and New Testaments (Hebrew and Greek respectively), but is a greater concern with the Old Testament.