Word of obligation (5)
I believe the answer is:
ought
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">word of obligation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ought that I've seen before include "Anything at all (archaic)" , "It expresses duty or obligation" , "Should, had, better" , "Verb implying duty; zero, nothing (archaic)" , "Strange thing" .)