Unshakable

Adjective

 * 1) That cannot be shaken or moved; unfaltering or unwavering.
 * 2) Having no errors or loopholes; unassailable.

Antonyms

 * shakable

Thesaurus
abiding, balanced, cool, fast, fiducial, firm, firm as Gibraltar, fixed, imperturbable, in equilibrium, predictable, reliable, secure, solid, sound, stable, steadfast, steady, substantial, unflappable, unflinching, unwavering, well-balanced, without nerves