Keeping inventory of just one of a pair of long socks (8)
I believe the answer is:
stocking
'keeping' is the definition.
'inventory of just one of a pair of long socks' is the wordplay.
I cannot really understand how this works, but
'inventory' could be 'stock' (synonyms) and 'stock' is present in the answer.
'one' could be 'i' (roman numeral) and 'i' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stocking that I've seen before include "a hang-up at Christmas?" , "Holding for sale" , "Keeping supplies of; item of wear" , "Leg wear" , "Woman's garment" .)