Marked by firm determination or resolution; not shakable.

synonyms: firm, steadfast, steady, stiff, unbendable, unfaltering, unwavering.

Roget 606: obstinate, tenacious, stubborn, obdurate, casehardened; inflexible etc. (hard) 323; balky; immovable, unshakable, not to be moved; inert etc. 172; unchangeable etc. 150; inexorable etc. (determined) 604; mulish, obstinate as a mule, pig-headed.    dogged; sullen, sulky; unmoved, uninfluenced unaffected.    willful, self-willed, perverse; resty^†, restive, restiff^†; pervicacious^†, wayward, refractory, unruly; heady, headstrong; entete [Fr.]; contumacious; crossgrained^†.    arbitrary, dogmatic, positive, bigoted; prejudiced etc. 481; creed-bound; prepossessed, infatuated; stiff-backed, stiff necked, stiff hearted; hard-mouthed, hidebound; unyielding; impervious, impracticable, inpersuasible^†; unpersuadable; intractable, untractable^†; incorrigible, deaf to advice, impervious to reason; crotchety etc. 608.    ... show more

Polish: niezachwiany, niewzruszony, niezłomny, nieugięty

Without flaws or loopholes.

synonyms: bulletproof, unassailable, watertight.