pertinacious (adj.)
- assiduous
- balking
- balky
- bigoted
- bullheaded
- case-hardened
- clamant
- clamorous
- constant
- continuing
- crying
- demanding
- diligent
- dogged
- dogmatic
- draining
- enduring
- exacting
- exigent
- exorbitant
- extortionate
- faithful
- fanatic
- fixed
- game
- gamy
- grasping
- gritty
- gutsy
- hardheaded
- headstrong
- immutable
- importunate
- inalterable
- indefatigable
- indomitable
- industrious
- insistent
- instant
- intolerant
- invincible
- lasting
- loud
- loyal
- mettlesome
- mulish
- nervy
- obstinate
- opinionated
- overzealous
- patient
- permanent
- persevering
- persistent
- persisting
- perverse
- pigheaded
- plodding
- plucky
- preoccupied
- pressing
- rapt
- red-blooded
- refractory
- relentless
- resolute
- restive
- sedulous
- self-willed
- set
- single-minded
- sleepless
- spirited
- spunky
- stable
- steadfast
- steady
- stiff-necked
- strong-willed
- stubborn
- sulky
- sullen
- taxing
- tenacious
- tireless
- tough
- unconquerable
- uncooperative
- undaunted
- undiscouraged
- unfailing
- unfaltering
- unflagging
- unflinching
- uninterrupted
- unregenerate
- unrelenting
- unremitting
- unshakable
- unsleeping
- unswerving
- untiring
- unwavering
- unwearied
- unwearying
- unyielding
- urgent
- willful
