IPA: /dɪˈbuːʃ/
KK: /dɪˈbuʃ/
To flow out from a narrow place into a larger area, often referring to water or to enter into a conflict or battle.
The river will debouche into the ocean after flowing through the valley.
Past: debouched
Past Participle: debouched
Debouche is derived from the Old French "de-" (meaning from or out of) and "bouche" (meaning mouth). The term originally referred to the act of flowing out of a narrow passage, like a river flowing out into a larger body of water, hence the meaning of the word as to emerge or to issue forth.
Think of something flowing 'out of' ('de-') a 'mouth' ('bouche') — that's why debouche means to emerge or come out.