Vocabulary of large person once idolised (7)
I believe the answer is:
lexicon
'vocabulary' is the definition.
(I know that vocabulary can be written as lexicon)
'large person once idolised' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'person once idolised' becomes 'exicon' (former icon).
'l'+'exicon'='LEXICON'
'of' is the link.
(Other definitions for lexicon that I've seen before include "Dictionary, especially of ancient languages" , "Dictionary of terms" , "set of terms" , "Dictionary as of Greek or Hebrew" , "Nice lox (anag)" .)