British lord, grand, a very long time in club (8)
I believe the answer is:
bludgeon
'club' is the definition.
(both can mean a heavy weapon)
'british lord grand a very long time' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'lord' becomes 'lud'.
'grand' becomes 'g' (G is short for grand as in a thousand).
'a very long time' becomes 'eon' (an extremely long period of time).
'b'+'lud'+'g'+'eon'='BLUDGEON'
'in' acts as a link.
(Other definitions for bludgeon that I've seen before include "Club used as a weapon" , "Bully; heavy weapon" , "Short stick with thickened end as weapon" , "Stick or club with a heavy end" , "Thick stick with a heavy end" .)