... bituminous material, initially to strengthen current ... (6)
I believe the answer is:
tarmac
'bituminous material' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'initially to strengthen current' is the wordplay.
'initially' says to take the initial letters.
'strengthen' becomes 'arm' (I can't justify this - if you can you should give a lot more credence to this answer).
'current' becomes 'ac' (alternating current).
The first letter of 'to' is 't'.
't'+'arm'+'ac'='TARMAC'
Can you help me to learn more?
(Other definitions for tarmac that I've seen before include "Road surface material of tar and stone" , "spread on airport runway" , "Surfaced area for plane to land" , "short runway, perhaps" , "Road-surfacing substance" .)