Sunnier seeing willow on leather, finally (6)
I believe the answer is:
rosier
'sunnier' is the definition.
Both the answer and definition are comparative adjectives. Perhaps there's an association between them I don't understand?
'willow on leather finally' is the wordplay.
'willow' becomes 'osier' (osier is a kind of willow).
'on' says to put letters next to each other.
'finally' suggests the final letters.
The final letter of 'leather' is 'r'.
'osier' put after 'r' is 'ROSIER'.
'seeing' is the link.
Can you help me to learn more?
(Other definitions for rosier that I've seen before include "looking more healthy" , "Brighter" , "More fortunate or hopeful" .)