Furnish the guys with top telegraphic apparatus (9)
I believe the answer is:
equipment
'apparatus' is the definition.
(I've seen this before)
'furnish the guys with top telegraphic' is the wordplay.
'furnish' becomes 'equip' (equipping is a kind of furnishing).
'the guys' becomes 'men' (guy can mean a man).
'with' means one lot of letters go next to another.
'top' suggests taking the first letters (in a down clue, the first letter is top).
The first letter of 'telegraphic' is 't'.
'equip'+'men'+'t'='EQUIPMENT'
(Other definitions for equipment that I've seen before include "Apparatus, gear" , "Kit, apparatus" , "Set of instruments that perform a service" , "outfit" , "Items needed for a particular purpose" .)