俱舍論頌疏論本 24.10

24.10

言一間者，間謂間隔，為有一生為間隔故，不證圓寂；或有一品惑為間隔故，不得不還果。由此二義，名一間也。

As for the expression ekavīcika ('one interval left'): vīci (interval) means separation. Because there is one rebirth serving as an interval, one does not realize complete cessation; or because there is one category of defilement serving as an interval, one does not attain the fruit of non-returner. Due to these two meanings, one is called an ekavīcika.