Alacrity

Promptness in response; cheerful readiness.

From Latin *alacritas* (liveliness, eagerness), from *alacer* (lively, brisk). The word carries a sense of *willing* quickness — not just speed, but speed delivered gladly.

Eagerness, briskness, readiness, promptness

Often paired with *with* (e.g. "with alacrity"). Implies the subject *welcomed* the task — distinguishes it from plain *speed*.