zealous
adj.adj. very eager and enthusiastic about something. You use this to describe someone who works hard and cares deeply about their job or beliefs.
adj. characterised by intense enthusiasm, eagerness, or devotion. Often used to describe a person's attitude toward a cause, a profession, or a set of beliefs.
She is a zealous supporter of the local football team.
The zealous lawyer worked through the night to prepare for the morning's hearing.
A zealous commitment to the project eventually led to burnout, as the team neglected their personal well-being in pursuit of an impossible deadline.
From Middle English zelose, from Latin zēlōsus, from zēlus + -ōsus, from Ancient Greek ζῆλος (zêlos, “zeal, jealousy”), from ζηλόω (zēlóō, “to emulate, to be jealous”). By surface analysis, zeal + -ous. Doublet of jealous.