Singletons (4)
'singletons?' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lonely hearts that I've seen before include "Unhappily unattached persons?" , "They need dates" , "singletons?" , "Singles" , "column in paper" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">singletons</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 ones that I've seen before include "Individuals" , "Units" , "1 & 1 & 1" , "Singletons" , "Aces" .)