Ancient city's river is omitted in plays (4)
I believe the answer is:
toys
'plays' is the definition.
(I've seen this before)
'ancient city's river is omitted' is the wordplay.
'ancient city's' becomes 'Troy's' (Troy was an ancient city).
'river' becomes 'r' (abbreviation).
'is omitted' suggests deleting specific letters.
'troys' with 'r' taken out is 'TOYS'.
'in' is the link.
(Other definitions for toys that I've seen before include "Chihuahuas?" , "Matters of no importance" , "Film" , "dolls, for example" , "Amusing items" .)