Romeo and Oscar have sex over August (5)
I believe the answer is:
royal
'august' is the definition.
(thesaurus)
'romeo and oscar have sex over' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'and' means one lot of letters go next to another.
'oscar' becomes 'o' (phonetic alphabet: alpha, bravo, charlie etc.).
'have sex' becomes 'lay'.
'over' says the letters should be written in reverse.
'lay' written backwards gives 'yal'.
'r'+'o'+'yal'='ROYAL'
(Other definitions for royal that I've seen before include "like The Grand Old Duke of York, perhaps" , "Imperial" , "Old gold coin -- stag with 12 or more points" , "one in palace?" , "William, say" .)