Yap about ewe's head and pull the wool over her eyes (5)
I believe the answer is:
cheat
'yap about ewe's head' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'pull the wool over her eyes' is the wordplay.
'pull the wool' becomes 'chat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'over' indicates putting letters inside.
'eyes' indicates the central letters (I've seen 'eye' mean this (eye can mean the centre of something)).
The middle letter of 'her' is 'e'.
'chat' going around 'e' is 'CHEAT'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for cheat that I've seen before include "Welsh" , "Trick or swindle" , "Play dishonestly" , "Fraud" , "Two-timer" .)