A pastry poet doesn't finish - that's rich (8)
I believe the answer is:
abundant
'rich' is the definition.
(similar in meaning)
'a pastry poet doesn't finish' is the wordplay.
'pastry' becomes 'bun'.
'poet' becomes 'dante' (13th- and 14th-century Italian poet).
'doesn't finish' means to remove the last letter.
'dante' with its final letter removed is 'dant'.
'a'+'bun'+'dant'='ABUNDANT'
'that's' is the link.
(Other definitions for abundant that I've seen before include "Existing in large quantities, plentiful" , "Plentiful, profuse" , "Plentiful, ample" , "well-provided" , "Exuberant" .)