Stick of wax candle, initially bit of light showing (6)
I believe the answer is:
crayon
'stick of wax' is the definition.
(I know that crayons are made from wax)
'candle initially bit of light showing' is the wordplay.
'initially' suggests taking the first letters.
'bit of light' becomes 'ray' (a ray of light).
'showing' becomes 'on' (as in a film showing or on at a cinema).
The initial letter of 'candle' is 'c'.
'c'+'ray'+'on'='CRAYON'
(Other definitions for crayon that I've seen before include "Wax pen" , "Drawing pen" , "alternative to charcoal" , "One colours with this" , "Pencil of chalk or wax" .)