Steals fifty-one paper planes, ultimately (5)
I believe the answer is:
lifts
'steals' is the definition.
(lifting is a kind of stealing)
'fifty-one paper planes ultimately' is the wordplay.
'fifty one' becomes 'LI' (Roman numerals).
'paper' becomes 'FT' (the Financial Times newspaper).
'ultimately' says to take the final letters.
The last letter of 'planes' is 's'.
'li'+'ft'+'s'='LIFTS'
(Other definitions for lifts that I've seen before include "Raises" , "Holds up" , "Elevates or elevators" , "Picks up" , "free transport" .)