The definition of solid is something which is sturdy and substantial or an object that isn't hollow.
The definition of adamant is someone who will never change his mind, or something that will never be changed.
Firmly in position; stationary:
That cannot be changed; fixed; unalterable
Firm in standing or position; not tottering or shaking; fixed; firm.
(Informal) Not easily excited or disconcerted; imperturbable; calm
(UK, slang) Good.
Not likely to change or be affected adversely; lasting; enduring
Forceful and pointed; emphatic:
Physically strong; vigorous; hardy
Strong; solid; firm; stout
Having or showing no doubt; positive; confident
Not easily moved or shaken
That cannot be misconstrued, refuted, defeated, nullified, etc.; flawless
Hard to bend or stretch; rigid; firm; not flexible or pliant
Certain; indestructible; permanent; steadfast; unaltering; unfaltering; unshakeable.
Find another word for unshakable. In this page you can discover 31 synonyms, antonyms, idiomatic expressions, and related words for unshakable, like: solid, adamant, firm, fixed, inflexible, steady, unflappable, unsinkable, unwavering, secure and sound.