Online connection device (5)
I believe the answer is:
modem
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">online connection device</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for modem that I've seen before include "Computer link" , "Device to connect computers by a telephone line" , "Computer interface" , "(Wireless) communication device" , "electronic device" .)