Smile -- spirit's about right! (4)
I believe the answer is:
grin
'smile' is the definition.
(grinning is a kind of smiling)
'spirit's about right' is the wordplay.
'spirit' becomes 'gin' (I've seen this before**).
'about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'gin' going around 'r' is 'GRIN'.
(Other definitions for grin that I've seen before include "Smile - all that could be seen of the vanishing Cheshire Cat" , "Look pleased" , "Toothy smile" , "Give a broad smile" , "Smirk" .)