Card cutter to double up (9)
I believe the answer is:
jackknife
'double up' is the definition.
(I've seen this before)
'card cutter' is the wordplay.
'card' becomes 'jack' (type of playing card).
'cutter' becomes 'knife' (knife is a kind of cutter).
'jack'+'knife'='JACKKNIFE'
'to' is the link.
(Other definitions for jackknife that I've seen before include "(Articulated) vehicular doubling up" , "Lose control on motorway, wrecking lorry" , "Cutter needed" , "Go out of control" , "Fold" .)