Notice worker eating cake that's rich (8)
I believe the answer is:
abundant
'rich' is the definition.
(similar in meaning)
'notice worker eating cake' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'worker' becomes 'ant' (worker is a type of ant).
'eating' means one lot of letters goes inside another.
'cake' becomes 'bun' (bun is a type of cake).
'ad'+'ant'='adant'
'adant' placed around 'bun' is 'ABUNDANT'.
'that's' acts as a link.
(Other definitions for abundant that I've seen before include "'Copious, galore (8)'" , "Plentiful, profuse" , "Exuberant" , "Present in great quantity" , "Plentiful, ample" .)