Puppy initially wanting assistance (5)
I believe the answer is:
whelp
'puppy' is the definition.
(I've seen this in another clue)
'initially wanting assistance' is the wordplay.
'initially' indicates taking the first letters.
'assistance' becomes 'help' (synonyms).
The first letter of 'wanting' is 'w'.
'w'+'help'='WHELP'
(Other definitions for whelp that I've seen before include "A young dog or puppy" , "Boy!" , "Puppy, cub" , "Young mammal" , "impudent young lad" .)