prelim vs preliminary exam

prelim and preliminary exam both are nouns.

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

As nouns, prelim and preliminary exam are synonyms defined as:

prelim and preliminary exam: an examination taken by graduate students to determine their fitness to continue

Other synonyms of prelim include preliminary examination.

prelim (noun)	preliminary exam (noun)
an examination taken by graduate students to determine their fitness to continue	an examination taken by graduate students to determine their fitness to continue
a minor match preceding the main event