leatherjacket vs leatherjack

leatherjacket and leatherjack both are nouns.

Word	Noun	Adjective	Verb	Adverb
leatherjacket	Yes	No	No	No
leatherjack	Yes	No	No	No

As nouns, leatherjacket and leatherjack are synonyms defined as:

leatherjacket and leatherjack: any of several New World tropical fishes having tiny embedded scales

leatherjacket (noun)	leatherjack (noun)
any of several brightly colored tropical filefishes	any of several New World tropical fishes having tiny embedded scales
any of several New World tropical fishes having tiny embedded scales
tough-skinned larva of certain crane flies