Advanced place among group of whales (7)
I believe the answer is:
posited
'advanced' is the definition.
(I've seen this before)
'place among group of whales' is the wordplay.
'place' becomes 'site' (synonyms).
'among' means one lot of letters goes inside another (inserted letters are placed among others).
'group of whales' becomes 'pod' (term for a group of whales).
'site' put inside 'pod' is 'POSITED'.
(Other definitions for posited that I've seen before include "Proposed as basis for argument" , "Suggested" , "Assumed" , "Topside (anag.)" , "Advanced" .)