Mike has no cap on very cold tooth (5)
I believe the answer is:
molar
'tooth' is the definition.
(I know that molar is a type of tooth)
'mike has no cap on very cold' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'has' says to put letters next to each other.
'no' becomes 'O' (resembles 0 - 'no' can mean 'zero').
'cap on very cold' becomes 'lar' (I can't explain this - if you can you should give a lot more credence to this answer).
'm'+'o'+'lar'='MOLAR'
Can you help me to learn more?
(Other definitions for molar that I've seen before include "Chewer and grinder" , "Grinding tooth in the back of a mammal's mouth" , "that could be capped" , "Moral (anag.)" , "of ivory, perhaps" .)