Come across heartless devil (4)
I believe the answer is:
find
'come across' is the definition.
(synonyms)
'heartless devil' is the wordplay.
'heartless' means to remove the middle letters.
'devil' becomes 'fiend' (synonyms).
'fiend' with its middle removed is 'FIND'.
(Other definitions for find that I've seen before include "Locate or discover" , "Encounter, locate" , "Discovery" , "Realise" , "Come across" .)