Gin neat when skipping tonic (7)
I believe the answer is:
gentian
'tonic' is the definition.
(tonic made from gentian roots)
'gin neat when skipping' is the wordplay.
'when skipping' is an anagram indicator (letters skip around).
'gin'+'neat'='ginneat'
'ginneat' is an anagram of 'GENTIAN'.
(Other definitions for gentian that I've seen before include "sort of violet" , "Mountain plant with blue bell-like flowers" , "Small deep blue flower" , "Violet's partner" , "Flower - antigen (anag)" .)