Plural of alacrity; multiple instances or types of eager, speedy, and lively action or readiness.
From alacrity (from Latin alacritas) with regular English plural -ies. In Latin it was already a mass noun (alacritas), but English pluralizes it to describe multiple instances.
It's really strange to pluralize alacrity because the word usually means an attitude or quality you either have or don't have—but technically you could have 'alacrities' if you showed enthusiasm in different situations!
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