Long facial hair, bald on top (4)
I believe the answer is:
ache
'long facial hair' is the definition.
'ache' can be an answer for 'long' (to long for something is to ache for it). I'm not sure about the 'facial hair' bit.
'bald on top' is the wordplay.
'bald' becomes 'ach' (I am not sure about this - if you are sure you should believe this answer much more).
'on' becomes 're' ('on' can be mean 'with reference to').
'top' means to remove the first letter.
're' with its initial letter taken away is 'e'.
'ach'+'e'='ACHE'
Can you help me to learn more?
(Other definitions for ache that I've seen before include "Twinge" , "Feel pain" , "Longing" , "strong feeling" , "painful" .)