Romeo in barrel to rotate (4)
I believe the answer is:
turn
'rotate' is the definition.
(I've seen this before)
'romeo in barrel' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'barrel' becomes 'tun' (tun is a kind of barrel).
'r' going inside 'tun' is 'TURN'.
'to' is the link.
(Other definitions for turn that I've seen before include "Go off - performance" , "Shape (using a lathe)" , "Start" , "Shift - wheel - round" , "Revolve; act" .)