Stockings, new, only ruined by son (6)
I believe the answer is:
nylons
'stockings' is the definition.
(I've seen this before)
'new only ruined by son' is the wordplay.
'new' becomes 'n'.
'ruined' indicates anagramming the letters.
'by' says to put letters next to each other.
'son' becomes 's'.
'only' anagrammed gives 'ylon'.
'n'+'ylon'+'s'='NYLONS'
(Other definitions for nylons that I've seen before include "Women's stockings made of synthetic fibre" , "Thin tights" , "Women's stockings made from a sheer material" , "Hosiery" , "Clothing" .)