Chilling midweek with Romeo, single sweetheart (5)
I believe the answer is:
eerie
'chilling' is the definition.
(I've seen this in another clue)
'midweek with romeo single sweetheart' is the wordplay.
'midweek' becomes 'ee'.
'with' is a charade indicator (letters next to each other).
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'single' becomes 'I' (one).
'sweetheart' becomes 'e' (the middle letter or heart of 'sweet').
'ee'+'r'+'i'+'e'='EERIE'
(Other definitions for eerie that I've seen before include "Unnerving" , "Unnatural" , "Strangely frightening" , "Scary, weird" , "Spooky, unearthly" .)