The time when an airplane, etc, is scheduled to depart.(noun)
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Use "time of departure" in a sentence
"He recognized with a sickening lurch that the time of departure was nigh; they were truly leaving this place behind, and with it Sean Cassada’s broken heart."
"Checking the log, he was told that the time of departure listed was precisely the same as the dispatcher's record."
"Then we passed the night as before; and when the time of departure drew near, I bethought me that Al Maamun would assuredly question me nor would ever be content save with a full explanation: so I said to her, ‘I see thee to be of those who delight in singing."