Boy welcoming English guide (4)
I believe the answer is:
lead
'guide' is the definition.
(synonyms)
'boy welcoming english' is the wordplay.
'boy' becomes 'lad' (informal term for boy).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'english' becomes 'E' (abbreviation).
'lad' going around 'e' is 'LEAD'.
(Other definitions for lead that I've seen before include "Guide by going in front" , "Guide the heavy metal" , "Top actor" , "Actor playing the principal role" , "Sort of poisoning" .)