Section includes a decoy (4)
I believe the answer is:
bait
'decoy' is the definition.
(synonyms)
'section includes a' is the wordplay.
'section' becomes 'bit' (both can mean part).
'includes' means one lot of letters goes inside another.
'bit' enclosing 'a' is 'BAIT'.
(Other definitions for bait that I've seen before include "Fishing lure" , "Enticement for fish" , "Lure; tease" , "Tempt" , "N in radio comms" .)