Fine soft fabric supplier (4)
I believe the answer is:
flax
'fabric supplier' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'fine soft' is the wordplay.
'fine' becomes 'f' (abbreviation in pencil classifications).
'soft' becomes 'lax' (synonyms).
'f'+'lax'='FLAX'
Can you help me to learn more?
(Other definitions for flax that I've seen before include "leaves from it make cloth" , "Plant cropped for linen" , "Fibre from a plant with blue flowers, used to make linen" , "Plant yielding linen" , "Plant from which linen is made" .)