One contrarily slicing odd bits of pine nut (5)
I believe the answer is:
pecan
'nut' is the definition.
(type of nut)
'one contrarily slicing odd bits of pine' is the wordplay.
'one' becomes 'ace' (ace has a value of one in some card games).
'contrarily' is a reversal indicator (letters in the opposite or contrary direction).
'slicing' means one lot of letters goes inside another (some letters slice into others).
'odd bits of' means one should take alternating letters.
The alternate letters of 'pine' are 'pn'.
'ace' in reverse letter order is 'eca'.
'eca' placed within 'pn' is 'PECAN'.
(Other definitions for pecan that I've seen before include "Type of nut" , "Nut with sweet oily kernel" , "Nut of American hickory tree" , "Smooth pinkish-brown nut, nice in pie" , "US nut tree" .)