Prone to disturb zho on trail (10)
I believe the answer is:
horizontal
'prone' is the definition.
(thesaurus)
'to disturb zho on trail' is the wordplay.
'to disturb' is an anagram indicator (I've seen 'disturbed' mean this).
'zho'+'on'+'trail'='zhoontrail'
'zhoontrail' is an anagram of 'HORIZONTAL'.
(Other definitions for horizontal that I've seen before include "Lying flat" , "even" , "Prone" , "What this answer isn't!" .)