cucumber vs gherkin

cucumber and gherkin both are nouns.

Word	Noun	Adjective	Verb	Adverb
cucumber	Yes	No	No	No
gherkin	Yes	No	No	No

As nouns, gherkin is a hyponym of cucumber; that is, gherkin is a word with a more specific, narrower meaning than cucumber:

cucumber: cylindrical green fruit with thin green rind and white flesh eaten as a vegetable; related to melons
gherkin: small prickly cucumber

cucumber (noun)	gherkin (noun)
cylindrical green fruit with thin green rind and white flesh eaten as a vegetable; related to melons	small prickly cucumber
a melon vine of the genus Cucumis; cultivated from earliest times for its cylindrical green fruit	any of various small cucumbers pickled whole