About five, it finished by making a hole (6)
I believe the answer is:
cavity
'a hole' is the definition.
(cavity is a kind of hole)
'about five it finished by' is the wordplay.
'about' is an insertion indicator.
'five' becomes 'V' (Roman numeral).
'finished by' becomes 'cay' (I can't explain this - if you can you should give a lot more credence to this answer).
'v'+'it'='vit'
'vit' going into 'cay' is 'CAVITY'.
'making' is the link.
Can you help me to learn more?
(Other definitions for cavity that I've seen before include "Hole, crater" , "Hollow place" , "Internal void" , "Small hole as in tooth" , "Decayed part of tooth" .)