inalterable (adj.)
- assiduous
- constant
- continuing
- diligent
- dogged
- enduring
- faithful
- fixed
- immovable
- immutable
- indefatigable
- indomitable
- industrious
- insistent
- invariable
- invincible
- lasting
- loyal
- obstinate
- patient
- permanent
- persevering
- persistent
- persisting
- pertinacious
- plodding
- preoccupied
- rapt
- relentless
- resolute
- sedulous
- single-minded
- sleepless
- stable
- steadfast
- steady
- stubborn
- tenacious
- tireless
- unalterable
- unchangeable
- unconquerable
- undaunted
- undiscouraged
- unfailing
- unfaltering
- unflagging
- unflinching
- uninterrupted
- unmodifiable
- unmovable
- unrelenting
- unremitting
- unsleeping
- unswerving
- untiring
- unwavering
- unwearied
- unwearying
