Wireless router accesses data -- internet opening starts (5)
I believe the answer is:
radio
'wireless' is the definition.
('radio' can be a synonym of 'wireless')
'router accesses data internet opening starts' is the wordplay.
'starts' says to take the initial letters.
The first letters of 'router accesses data internet opening' is 'RADIO'.
(Other definitions for radio that I've seen before include "Communicate with" , "send a message" , "Receiving device" , "listening device" , "Sound receiver" .)