1 idle

2 lazy

1 invulnerable

1 untiring

2 unremitting

3 indefatigable

1 inert (chemistry)

2 apathy

3 inertia

4 laziness

1 slack

2 lazy

3 remiss

1 to persevere unremittingly (idiom); to keep going until the end

1 to work from morning to night (idiom)

1 avoid the enemy when he is fresh and strike him when he is tired and withdraws (idiom)