Umbrella when it's overcast for show (9)
I believe the answer is:
broadcast
'for show' is the definition.
(broadcast is a kind of show)
'umbrella when it's overcast' is the wordplay.
I cannot really understand how this works, but
'when' could be 'as' (eg 'when I walked' means 'as I walked') and 'as' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for broadcast that I've seen before include "distributed by hand" , "Send out by radio or television" , "Send out over the airwaves" , "Show" , "Transmit over airwaves" .)