Without Egypt's capital Egyptian river is nothing (3)
I believe the answer is:
nil
'is nothing' is the definition.
(eg nil is zero in football)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nil that I've seen before include "Nothing - in Latin" , "Nothing found in senility" , "There's nothing left" , "Non-existent" , "Nothing, no value" .)