Fastening material concealed by level crossing (6)
I believe the answer is:
velcro
'fastening material' is the definition.
(I've seen this before)
'concealed by level crossing' is the wordplay.
'concealed' indicates a hidden word.
'VELCRO' is hidden in the letters of 'by level crossing'.
(Other definitions for velcro that I've seen before include "In clover with cloth fastener" , "Clothes fastener made with two strips of material" , "It fastens" , "Clothes fastener of two pieces of cloth that stick" , "Two strips with tiny hooks and eyes for fastening" .)