Etymology
Advertisement
inflexible (adj.)

late 14c., "incapable of being bent, physically rigid," also figuratively, "unyielding in temper or purpose," from Old French inflexible and directly from Latin inflexibilis "that cannot be bent," from in- "not, opposite of" (see in- (1)) + flexibilis "pliant, yielding" (see flexible). In early 15c. an identical word had an opposite sense, "capable of being swayed or moved," from the other in- "in, on" (see in- (2)). Related: Inflexibly.

Related entries & more 
Advertisement
adamantine (adj.)
"made of adamant; having the qualities of adamant" (hard, unyielding, unbreakable, inflexible), c. 1200, from Latin adamantinus "hard as steel, inflexible," from Greek adamantinos "hard as adamant," from adamas (genitive adamantos) "unbreakable, inflexible," as a noun, "hardest material" (see adamant (n.)).
Related entries & more 
obstinacy (n.)

late 14c., obstinacie, "hardness of heart, inflexibility of temper or purpose," from Medieval Latin obstinatia, from obstinatus "resolute, inflexible, stubborn" (see obstinate).

Related entries & more 
ostinato 

in musical phrases, "recurring frequently, repeated," 1876, from Italian ostinato "obstinate, persistent," from Latin obstinatus "resolute, resolved, determined, inflexible, stubborn," past participle of obstinare "to persist" (see obstinate). 

Related entries & more 
Advertisement
stiff (adj.)

Old English stif "rigid, inflexible," from Proto-Germanic *stifaz "inflexible" (source also of Dutch stijf, Old High German stif, German steif "stiff;" Old Norse stifla "choke"), from PIE *stipos-, from root *steip- "press together, pack, cram" (source also of Sanskrit styayate "coagulates," stima "slow;" Greek stia, stion "small stone," steibo "press together;" Latin stipare "pack down, press," stipes "post, tree trunk;" Lithuanian stipti "to stiffen, grow rigid," stiprus "strong;" Old Church Slavonic stena "wall"). Of battles and competitions, from mid-13c.; of liquor, from 1813. To keep a stiff upper lip is attested from 1815. Related: Stiffly.

Related entries & more 
unbend (v.)
mid-13c., "relax a bow by unstringing it," from un- (2) "reverse, opposite of" + bend (v.). Intransitive sense from 1746. Figurative meaning "to become genial, relax" (1748) has a sense opposite to that of unbending "inflexible, obstinate" (1680s), which does not derive from the bow-stringing image.
Related entries & more 
atropine (n.)
also atropin, "poisonous crystalline alkaloid obtained from nightshade," 1831, from Latin atropa "deadly nightshade" (from which the alkaloid poison is extracted), from Greek atropos "inflexible, unchangeable," also the name of one of the Fates (see Atropos) + chemical suffix -ine (2). By 1821 in French and German.
Related entries & more 
Rhadamanthus (n.)

name of one of the three judges of the Underworld in Greek mythology, son of Zeus and Europa, from Latinized form of Greek Rhadamanthos, whose name seems to contain Greek rhadamos "branch, twig, shoot." Used in English from 1580s allusively of inflexible judges or solid and final judgment. Related: Rhadamantine; Rhadamanthean.

Related entries & more 
obstinate (adj.)

"stubborn in adhering to one's own course, unyielding," late 14c., from Latin obstinatus "resolute, resolved, determined, inflexible, stubborn," past participle of obstinare "persist, stand stubbornly, set one's mind on," from ob "by" (see ob-) + stinare (related to stare "stand"), from PIE *ste-no-, from root *sta- "to stand, make or be firm." Related: Obstinately.

Related entries & more