Note tip from naturalist for boy (3)
I believe the answer is:
son
'boy' is the definition.
(male child)
'note tip from naturalist' is the wordplay.
'note' becomes 'so' (musical note).
'tip from' says to take the initial letters.
The first letter of 'naturalist' is 'n'.
'so'+'n'='SON'
'for' acts as a link.
(Other definitions for son that I've seen before include "Heir" , "Male child" , "Male descendant" , "Male scion" , "A relative" .)