Frank and Oscar exercise before noon (4)
I believe the answer is:
open
'frank' is the definition.
(synonyms)
'oscar exercise before noon' is the wordplay.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'exercise' becomes 'pe' (Physical Education).
'before' means one lot of letters go next to another.
'noon' becomes 'n'.
'o'+'pe'+'n'='OPEN'
'and' is the link.
(Other definitions for open that I've seen before include "Plain" , "ready to entertain new ideas" , "golf contest" , "Frank, candid" , "Candid - ready for business" .)