This is the 9487th most frequent French word.
débouchait
"Débouchait" means "was emerging" or "was opening out."
In this sentence, 'débouchait' means 'was uncorking,' describing the past tense action of removing a cork from a wine bottle.
Il débouchait une bouteille de vin pour le dîner.
He was uncorking a bottle of wine for dinner.
Here, 'débouchait' is used to signify 'flowed out,' indicating the past tense of an ongoing action of emerging into an open area.
La rivière débouchait dans une vaste plaine verdoyante.
The river flowed out into a vast green plain.
In this instance, 'débouchait' conveys the meaning of 'opened up,' describing the past tense action where the tunnel became visible to them.