tireless (adj.)
- active
- ardent
- assiduous
- constant
- continuing
- determined
- diligent
- dogged
- dynamic
- enduring
- energetic
- enthusiastic
- faithful
- fervent
- hard
- hardworking
- immutable
- inalterable
- indefatigable
- indomitable
- industrious
- inexhaustible
- insistent
- invincible
- laborious
- lasting
- lively
- loyal
- obstinate
- patient
- permanent
- persevering
- persistent
- persisting
- pertinacious
- plodding
- preoccupied
- rapt
- relentless
- resolute
- sagging
- sedulous
- single-minded
- sleepless
- spirited
- stable
- staunch
- steadfast
- steady
- strenuous
- stubborn
- tenacious
- unconquerable
- undaunted
- undeviating
- undiscouraged
- unfailing
- unfaltering
- unflagging
- unflinching
- uninterrupted
- unrelenting
- unremitting
- unsleeping
- unsparing
- unswerving
- untiring
- unwavering
- unwearied
- unwearying
- vehement
- vigorous
- vital
- zealous
