Hesitate, tired out crossing top of hill (6)
I believe the answer is:
dither
'hesitate' is the definition.
(thesaurus)
'tired out crossing top of hill' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'crossing' means one lot of letters goes inside another.
'top of' suggests taking the first letters.
The first letter of 'hill' is 'h'.
'tired' with letters rearranged gives 'diter'.
'diter' enclosing 'h' is 'DITHER'.
(Other definitions for dither that I've seen before include "Vacillate, be undecided" , "perturbation" , "Waver, vacillate" , "Hestitate indecisively" , "Hesitate indecisively, vacillate" .)