Part of neck line in linen (6)
I believe the answer is:
napery
'linen' is the definition.
(napery is a kind of linen)
'part of neck line' is the wordplay.
'part of neck' becomes 'nape' ('nape' is part of 'neck').
'line' becomes 'ry' (abbreviation for railway).
'nape'+'ry'='NAPERY'
'in' is the link.
(Other definitions for napery that I've seen before include "Fine table linen" , "Heavy white table linen" , "Linens for the dining table" , "Tablecloths, napkins etc" , "Scots tablecloth" .)