Head of lettuce swallowed by audacious pet (7)
I believe the answer is:
darling
'pet' is the definition.
(I know that pet can be written as darling)
'head of lettuce swallowed by audacious' is the wordplay.
'head of' suggests taking the first letters.
'swallowed by' is an insertion indicator.
'audacious' becomes 'daring' (audacious means daring or adventurous).
The first letter of 'lettuce' is 'l'.
'l' placed into 'daring' is 'DARLING'.
(Other definitions for darling that I've seen before include "Adorable - honeybun" , "Wendy's family (Peter Pan)" , "Beloved" , "family in play" , "Victorian heroine" .)