Superlatively neat, is very keen to stuff bird (7)
I believe the answer is:
tidiest
'superlatively neat' is the definition.
I can't tell whether this definition defines the answer.
'very keen to stuff bird' is the wordplay.
'very keen' becomes 'dies' (I can't justify this - if you can you should believe this answer much more).
'to stuff' indicates putting letters inside (some letters stuff into others).
'bird' becomes 'tit' (tit is a kind of bird).
'dies' placed inside 'tit' is 'TIDIEST'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for tidiest that I've seen before include "smarter than anything" , "One orderly more than others" , "Neatest" , "optimally arranged" , "most trim" .)