Old Bob ill, out on the briny? (7)
I believe the answer is:
sailing
'out on the briny?' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'old bob ill' is the wordplay.
'old bob' becomes 's' (abbreviation for bob or shilling used before 1971).
'ill' becomes 'ailing' (similar in meaning).
's'+'ailing'='SAILING'
Can you help me to learn more?
(Other definitions for sailing that I've seen before include "Marine sport" , "Eg, yachting" , "event" , "Water sport" , "Going by, eg, yacht" .)