adjectival noun or quasi-adjective, noun

Messages.yoji.
  1. indomitable perseverance, invincible fortitude.

Variations

Pronunciation Kanji Kana Is Common
堅忍不抜 けんにんふばつ

Contained Kanji Breakdown

strict, hard, solid
ケン かた.い きん (Early Jr. High, N1)
hard, wise
カン ケン コウ
retainer, subject
シン とみ おみ (4th, N2)
or again, furthermore, on the other hand
また ユウ やす (Late Jr. High, N1)
soil, earth, ground
ド つち は (1st, N5)
endure, bear, put up with
ニン しの.ぶ おし (Early High School, N1)
blade, sword, edge
は ジン やいば (Early High School, N1)
sword, saber, knife
かたな トウ ち (2nd, N1)
dot, tick or dot radical (no. 3)
チュ (Kentei 1)
heart, mind, spirit
こころ シン (2nd, N4)
negative, non-, bad
 (4th, N4)
cliff, (厂 variant)
divining, fortune-telling, divination or katakana to radical (no. 25)
ボク うらな.う うらない (Kentei Pre-1)
slip out, extract, pull out
ぬ.く バツ ぬき (Early Jr. High, N3)
hand, hand radical (no. 64)
シュ
friend
とも ユウ う (2nd, N5)
left hand, cliff(厂) variant
or again, furthermore, on the other hand
また ユウ やす (Late Jr. High, N1)