Frustrated as Old Penny is taken on (12)
I believe the answer is:
disappointed
'frustrated' is the definition.
(disappointing is a kind of frustrating)
'old penny is taken on' is the wordplay.
'old penny' becomes 'd'.
'taken on' becomes 'appointed' (I've seen this before).
'd'+'is'+'appointed'='DISAPPOINTED'
'as' acts as a link.
(Other definitions for disappointed that I've seen before include "Sad and let-down" , "Let down" , "Saddened" , "Unhappy" , "Feeling sad" .)