釋氏要覽 3.180

3.180

梵語具云迦栗提迦。即九月望宿名也。謂西國三月安居。至九月十六日解。後安居比丘行化故。取望宿為名也。

In Sanskrit, it is fully called Kārttika. That is the name of the full-moon lunar mansion of the ninth month. It means that in the Western Realm, the three-month retreat dissolves on the sixteenth day of the ninth month, and because the monks of the later retreat go about to convert beings, it takes its name from this full-moon lunar mansion.