Lord North's warning? (5)
I believe the answer is:
siren
'warning?' is the definition.
(thesaurus)
'lord north's' is the wordplay.
'lord' becomes 'sire' (sire is a kind of lord).
'north' becomes 'n' ('N' can be a synonym of 'north').
'sire'+'n'='SIREN'
(Other definitions for siren that I've seen before include "Bewitching singer,part- woman, part-bird" , "Loud warning device" , "Risen like Lorelei" , "Temptress; warning signal" , "Rinse (anag) - sea nymph" .)