A lassie turned out to have other names (7)
I believe the answer is:
aliases
'other names' is the definition.
(I've seen this in another clue)
'a lassie turned out' is the wordplay.
'turned out' indicates an anagram (turn out can mean to organise).
'lassie' is an anagram of 'liases'.
'a'+'liases'='ALIASES'
'to have' is the link.
(Other definitions for aliases that I've seen before include "Assumed names" , "handles affected?" , "Sobriquets" , "False identities" , "Pseudonyms" .)