Came across a number employed in making roads (5)
I believe the answer is:
metal
'employed in making roads' is the definition.
(I've seen this before)
'came across a number' is the wordplay.
'came across' becomes 'met' ('meet' can be a synonym of 'come across').
'number' becomes 'l' (L is an example).
'met'+'a'+'l'='METAL'
(Other definitions for metal that I've seen before include "Copper, perhaps" , "Lead, say" , "Lead or iron, perhaps" , "Maybe copper" , "Broken stone used in road-making" .)