Wi-Fi device (5)
(Other definitions for modem that I've seen before include "Connector for computer to telephone line" , "Telephonic computer connection" , "Phone-to-computer connector" , "Communications device" , "Computer/line connector" .)
'wi-fi device' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for router that I've seen before include "Emphatic winner" , "device fitted to computer" , "Carpenter's power tool; data forwarder" , "that easily beats the competition" , "Device that forwards data between computer networks" .)