Romeo gets in girl's hair (5)
I believe the answer is:
tress
'hair' is the definition.
(I know that tress is a type of coif)
'romeo gets in girl's' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'gets in' means one lot of letters goes inside another.
'girl' becomes 'tess' (girl's name).
'r' inserted inside 'tess' is 'TRESS'.
(Other definitions for tress that I've seen before include "Rests (anag.)" , "Switch" , "Curl - lock" , "Bit of hair" , "Obsolete support" .)