Long story about Eeyore’s tail (5)
I believe the answer is:
yearn
'long' is the definition.
('yearn' can be a synonym of 'long')
'story about eeyore's tail' is the wordplay.
'story' becomes 'yarn' ('yarn' can be a synonym of 'story').
'about' means one lot of letters goes inside another.
'tail' suggests the final letters.
The final letter of 'eeyore' is 'e'.
'yarn' placed around 'e' is 'YEARN'.
(Other definitions for yearn that I've seen before include "Mark of injury" , "wish" , "Long (for something)" , "Have a great longing" , "Desire strongly" .)