Standard answer for old invaders (7)
I believe the answer is:
normans
'old invaders' is the definition.
(invaders of England in 1066)
'standard answer' is the wordplay.
'standard' becomes 'norm' (norm is a kind of standard).
'answer' becomes 'ans' (abbreviation for answer).
'norm'+'ans'='NORMANS'
'for' is the link.
(Other definitions for normans that I've seen before include "11th century invaders" , "belonging to Greg the golfer?" , "Some Frenchmen" , "French folk" , "Our last successful invaders" .)