zealous
ZEL-usadjMeaning full of eager devotion to a cause or task
Memory hook ZEAL-ous: full of ZEAL, A to Z. Omar sorts every can, bottle and scrap of paper into the right bin and cheers each one in. His zeal for recycling makes him zealous.
The zealous volunteers cleaned the whole beach before breakfast.
In context Most of the club recycled when it was convenient, but Omar was zealous about it: he sorted every scrap, rinsed every can and reminded everyone else to do the same.
Similar devoted, passionate, fervent, enthusiastic
Opposite apathetic, indifferent, halfhearted
From zeal, from Greek zelos, “eagerness, fervor.”