Mix gin and tonic love, secretly (9)
I believe the answer is:
incognito
'secretly' is the definition.
(thesaurus)
'mix gin and tonic love' is the wordplay.
'mix' indicates an anagram.
'and' is a charade indicator (letters next to each other) (I've seen this in other clues).
'love' becomes 'o' (In tennis, 'love' means 'zero').
'gin' put after 'tonic' is 'tonicgin'.
'tonicgin' anagrammed gives 'incognit'.
'incognit'+'o'='INCOGNITO'
(Other definitions for incognito that I've seen before include "with unknown identity" , "as disguised person appears?" , "With identity kept secret, perhaps travelling thus" , "under another name" , "Keeping one's identity a secret" .)