Raise 51 feet (4)
I believe the answer is:
lift
'raise' is the definition.
('lift' can be a synonym of 'raise')
'51 feet' is the wordplay.
'51' becomes 'li' (roman numeral).
'feet' becomes 'ft' (I've seen this in other clues).
'li'+'ft'='LIFT'
(Other definitions for lift that I've seen before include "remove" , "encouragement" , "Raise; elevator" , "Take" , "Steal (colloq.); elevator" .)