Formal promise (6)
(Other definitions for guarantee that I've seen before include "Formal assurance" , "Underwrite; promise with certainty" , "Provide financial security for" , "Undertake" , "Written assurance, pledge" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">formal promise</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 oath that I've seen before include "Curse or solemn word" , "A curse or solemn declaration" , "darn, for example" , "A word with a witness" , "word intended?" .)
(Other definitions for pledge that I've seen before include "Solemn promise" , "Plight" , "assurance" , "Deposit" , "make toast" .)