Seethe as whiskey taken from bather? (6)
I believe the answer is:
simmer
'seethe' is the definition.
(I've seen this before)
'whiskey taken from bather?' is the wordplay.
'whiskey' becomes 'w' (alpha bravo charlie delta ...).
'taken from' is a deletion indicator.
'bather?' becomes 'swimmer' ('swimmer' can be a synonym of 'bather').
'swimmer' with 'w' taken out is 'SIMMER'.
'as' is the link.
(Other definitions for simmer that I've seen before include "Cook just below boiling point" , "Bubble on a low gas" , "Cook in gently boiling water" , "Keep liquid just below boiling point" , "Gently boil" .)