Old English eallmæst "nearly all, for the most part," literally "mostly all;" see all + most. Modern form is from 15c. The original sense is now typically expressed by almost all; sense of "very nearly, all but" is from c. 1200.
the baby was almost asleep when the alarm sounded
we're almost finished
Almohades
almond
almoner
almonry
Almoravides
almost
alms
alms-house
aloe
aloft
aloha