Romeo in perfect terror (5)
I believe the answer is:
dread
'terror' is the definition.
(I've seen this before)
'romeo in perfect' is the wordplay.
'romeo' becomes 'R' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' indicates putting letters inside.
'perfect' becomes 'dead' (eg in phrases like 'dead centre').
'r' inserted inside 'dead' is 'DREAD'.
(Other definitions for dread that I've seen before include "Anticipate with fear" , "great anxiety" , "Intense fear" , "alarm" , "Dared to fear greatly" .)