Act on gold measure threshold (8)
I believe the answer is:
doorstep
'threshold' is the definition.
('doorstep' can be a synonym of 'threshold')
'act on gold measure' is the wordplay.
'act on' becomes 'do'.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'measure' becomes 'step' (step is a kind of measure**).
'do'+'or'+'step'='DOORSTEP'
(Other definitions for doorstep that I've seen before include "Try some canvassing" , "go canvassing" , "slab at threshold" , "Canvass locally" , "To conduct house-to-house interviews" .)