Firm paid for jet (5)
I believe the answer is:
comet
'jet' is the definition.
(I've seen this before)
'firm paid' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'paid' becomes 'met' (I've seen this in other clues).
'co'+'met'='COMET'
'for' acts as a link.
(Other definitions for comet that I've seen before include "Small heavenly body" , "Heavenly visitor" , "high-flier" , "Celestial orbiter" , "Long distance traveller" .)