Cheer about having nothing, to be consistent (6)
I believe the answer is:
cohere
'be consistent' is the definition.
(I've seen this before)
'cheer about having nothing' is the wordplay.
'about' indicates an anagram.
'having' is an insertion indicator.
'nothing' becomes 'O' (looks like zero - 0).
'cheer' anagrammed gives 'chere'.
'chere' placed around 'o' is 'COHERE'.
'to' acts as a link.
(Other definitions for cohere that I've seen before include "Stick together, remain united" , "Be consistent" , "Cling" , "Hold firmly together" , "Stick firmly together" .)