Wireless router's last two bits connected by plug (5)
I believe the answer is:
radio
'wireless' is the definition.
(synonyms)
'router's last two bits connected by plug' is the wordplay.
'last' indicates one should take the final letters.
'two bits' becomes 'IO' (1 and 0 are two bits in computing).
'connected by' means one lot of letters goes inside another (inserted letters connect other letters together).
'plug' becomes 'ad' (as in plugging a product).
The final letter of 'router' is 'r'.
'r'+'io'='rio'
'rio' placed around 'ad' is 'RADIO'.
(Other definitions for radio that I've seen before include "Sound receiver" , "Electronic receiver" , "Receiving apparatus" , "Transistor" , "Transmitter" .)