False name used by pal I assisted (5)
I believe the answer is:
alias
'false name' is the definition.
(synonyms)
'used by pal i assisted' is the wordplay.
'used by' says the answer is hidden in the clue.
'ALIAS' can be found hidden inside 'pal i assisted'.
(Other definitions for alias that I've seen before include "Assumed identity" , "another name" , "it may be assumed" , "A sail (anag)" , "Alternative identity" .)