The definition of alacrity means joyful willingness or readiness.(noun)
Someone quickly and cheerfully accepting an invitation to a wedding is an example of a person acting with alacrity.
See alacrity in Webster's New World College Dictionary
Origin: ME & OFr alacrite < Lalacritas, liveliness < alacer, lively
See alacrity in American Heritage Dictionary 4
Origin: Latin alacritās
Origin: , from alacer, lively.
Learn more about alacrity