Allhallowmas

1. All Saints' Day.
2. The feast observed on All Saints' Day.

[Middle English Alhalwemesse, from Old English ealra hālgena mæsse : ealra, genitive pl. of eall, all; see all + hālgena, genitive pl. of hālga, saint (from hālig, holy; see holy) + mæsse, Mass; see Mass.]