A feature held by gear wheel for guidance (8)
I believe the answer is:
coaching
'for guidance' is the definition.
(thesaurus)
'a feature held by gear wheel' is the wordplay.
'feature' becomes 'chin' (facial feature).
'held by' means one lot of letters goes inside another.
'gear wheel' becomes 'cog' (I've seen this in another clue).
'a'+'chin'='achin'
'achin' inserted inside 'cog' is 'COACHING'.
(Other definitions for coaching that I've seen before include "tuition" , "Tutoring" , "Sports instructing or training" , "Training, teaching" .)