Procrastinated, which is indeed unprofessional (7)
I believe the answer is:
'procrastinated' is the definition.
The answer and definition can be both to do with fundamental existence as well as being past participle verbs.
Perhaps you can see an association between them that I can't see?
'indeed unprofessional' is the wordplay.
I cannot quite see how this works, but
'indeed' could be 'aye' (I've seen this before) and 'aye' is present in the answer.
This explanation may well be incorrect...
'which is' is the link.
Can you help me to learn more?
(Other definitions for delayed that I've seen before include "Put back" , "Made late" , "Held up, back" , "Protracted" , "Detained, help up" .)