It's not free of charge (3)
I believe the answer is:
ion
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">it's not free of charge</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ion that I've seen before include "Electrically-charged particle" , "Electrically charged particle" , "Charged atom/molecule" , "Electrically charged atom or group of atoms" , "Eletrically charged particle" .)