A bit of an ear and most of a sphere (4)
I believe the answer is:
lobe
'a sphere' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'a bit of an ear and most' is the wordplay.
'a bit of' suggests taking the first letters.
'and' means one lot of letters go next to another.
'most' becomes 'lob' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'ear' is 'e'.
'e' after 'lob' is 'LOBE'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for lobe that I've seen before include "Piece of ear" , "Base of ear" , "Lower part of the ear" , "could be site of a 24 [STUD]" , "part of brain" .)