I had lunch outside King’s Cross (5)
I believe the answer is:
irate
'cross' is the definition.
(both can mean angry)
'i had lunch outside king's' is the wordplay.
'had lunch' becomes 'ate' (I've seen this in another clue).
'outside' means one lot of letters goes inside another (some letters go outside others).
'king' becomes 'R' (abbreviation of Latin rex).
'i'+'ate'='iate'
'iate' enclosing 'r' is 'IRATE'.
(Other definitions for irate that I've seen before include "Angry - furious" , "Extremely angry" , "having got in wax" , "Full of 22" , "Livid" .)