One choosing e-reader? (7)
I believe the answer is:
elector
'one choosing' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'e-reader?' is the wordplay.
'reader?' becomes 'lector' ('lector' can be a synonym of 'reader').
'e'+'lector'='ELECTOR'
Can you help me to learn more?
(Other definitions for elector that I've seen before include "One crossing" , "A prince of the Holy Roman Empire" , "might he make one cross?" , "One whom may vote" , "Constituent" .)