Source : Webster's Revised Unabridged Dictionary (1913)

Gherkin \Gher"kin\ (g[~e]r"k[i^]n), n. [D. agurkje, a dim. akin
   to G. gurke, Dan. agurke; cf. Pol. og['o]rek, Bohem. okurka,
   LGr. 'aggoy`rion watermelon, Ar. al-khiy[=a]r, Per.
   khiy[=a]r.]
   1. (Bot.) A kind of small, prickly cucumber, much used for
      pickles.

   2. (Zo["o]l.) See {Sea gherkin}.

Source : WordNet®

gherkin
     n 1: any of various small cucumbers pickled whole
     2: small prickly cucumber