Nonplussed (2,1,4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nonplussed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for at a loss that I've seen before include "Puzzled, bewildered" , "(Running) in deficit" , "how incompetent companies can operate" , "Puzzled - below cost" , "Puzzled and indecisive? No profit in it" .)
(Other definitions for at sea that I've seen before include "Worse things can happen here" , "Lost or confused - on the briny?" , "In confusion" , "stumped" , "disorientated" .)