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' is an anagram indicator.
'about' means one lot of letters goes inside another.
'start' says to take the initial letters.
The initial letter of 'poor' is 'p'.
'curse' is an anagram of 'sruce'.
'sruce' placed around '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" .)