Transport from Britain to America (3)
I believe the answer is:
bus
'transport' is the definition.
(bus is a kind of transport)
'britain to america' is the wordplay.
'britain' becomes 'b' (common abbreviation as in GB).
'to america' becomes 'us' (abbreviation for the United States).
'b'+'us'='BUS'
'from' is the link.
(Other definitions for bus that I've seen before include "Public transport vehicle" , "Mode of public transport" , "Of projectiles; (go) mad (slang)" , "Coach" , "Large passenger vehicle - small business!" .)