prelim vs exam

prelim and exam both are nouns.

Word	Noun	Adjective	Verb	Adverb
prelim	Yes	No	No	No
exam	Yes	No	No	No

As nouns, exam is a hypernym of prelim; that is, exam is a word with a broader meaning than prelim:

prelim: an examination taken by graduate students to determine their fitness to continue
exam: a set of questions or exercises evaluating skill or knowledge

Other hypernyms of prelim include examination, test.

prelim (noun)	exam (noun)
an examination taken by graduate students to determine their fitness to continue	a set of questions or exercises evaluating skill or knowledge
a minor match preceding the main event