Brother nowadays reluctant to stock initially coarse fabric (10)
I believe the answer is:
broadcloth
'fabric' is the definition.
(I know that broadcloth is a type of fabric)
'brother nowadays reluctant to stock initially coarse' is the wordplay.
'brother' becomes 'bro' (short for brother).
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'reluctant' becomes 'loth' (if you are loth to do something you are reluctant).
'to stock' is an insertion indicator (some letters contain or stock others).
'initially' says to take the initial letters.
The first letter of 'coarse' is 'c'.
'ad'+'loth'='adloth'
'adloth' enclosing 'c' is 'adcloth'.
'bro'+'adcloth'='BROADCLOTH'
(Another definition for broadcloth that I've seen is " material".)