Timid look on learner cutting wood (6)
I believe the answer is:
yellow
'timid' is the definition.
(thesaurus)
'look on learner cutting wood' is the wordplay.
'look' becomes 'lo' (archaic term meaning 'look!').
'on' indicates putting letters inside.
'learner' becomes 'l'.
'cutting' is an insertion indicator (some letters cut their way into a word).
'wood' becomes 'yew' (yew is a kind of wood).
'l' inserted inside 'yew' is 'yelw'.
'lo' going within 'yelw' is 'YELLOW'.
(Other definitions for yellow that I've seen before include "This card is shown by soccer referee as a caution" , "Colour of sunflowers and ripe lemons" , "Primrose-coloured" , "likely to run" , "'Caution' colour" .)