The term 'with the mouth wide open' can be summarized by two crossword solutions: AGAPE (5 letters) and GAPINGLY (8 letters). AGAPE is an adjective that means 'open-mouthed' or 'wide-eyed with wonder or astonishment'. GAPINGLY is an adverb that means 'in a manner that involves having the mouth wide open'. Both words are used to describe a situation where someone's mouth is wide open, usually in surprise or awe.