Father gets new warning (5)
I believe the answer is:
siren
'warning' is the definition.
(thesaurus)
'father gets new' is the wordplay.
'father' becomes 'sire' ('sire' can be a synonym of 'father').
'gets' says to put letters next to each other.
'new' becomes 'n'.
'sire'+'n'='SIREN'
(Other definitions for siren that I've seen before include "Loud whistle or sea witch" , "Device producing a loud wailing sound as a signal" , "Vamp; alarm" , "Temptress; warning signal" , "Dangerously fascinating woman" .)