A type lacking finish is similar (4)
I believe the answer is:
akin
'is similar' is the definition.
(similar in meaning)
'a type' is the wordplay.
'type' becomes 'kin' (I can't justify this - if you can you should believe this answer much more).
'a'+'kin'='AKIN'
'lacking finish' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for akin that I've seen before include "not totally similar" , "Of similar character" , "Of like nature or related" , "Related by blood" , "Of a similar nature" .)