Being smart, curse wildly about a poor start (6)
I believe the answer is:
spruce
'being smart' is the definition.
(synonyms)
'curse wildly about a poor start' is the wordplay.
'wildly' indicates an anagram.
'about' indicates putting letters inside.
'start' indicates taking the first letters.
The initial letter of 'poor' is 'p'.
'curse' anagrammed gives 'sruce'.
'sruce' enclosing 'p' is 'SPRUCE'.
(Other definitions for spruce that I've seen before include "Smart in appearance like fir tree" , "Smart and tidy - tree" , "Smart, trim" , "Well-groomed - tree" , "Evergreen pyramid-shaped tree" .)