Wholeheartedly premature about a snug place (9)
I believe the answer is:
earnestly
'wholeheartedly' is the definition.
(thesaurus)
'premature about a snug place' is the wordplay.
'premature' becomes 'early' (similar in meaning).
'about' is an insertion indicator.
'a snug place' becomes 'nest' (I've seen this in another clue).
'early' going around 'nest' is 'EARNESTLY'.
(Other definitions for earnestly that I've seen before include "Zealously" , "Sincerely and seriously" , "how Wilde character may be acted?" , "Relent, say, in sincere and serious manner" , "Showing commitment" .)