stable

Synonyms: abiding anchored balanced brick-wall calm deeprooted durable enduring equable established even fast firm immutable invariable lasting nailed perdurable permanent poised reliable resolute safe secure set set in stone solid solid as a rock sound stabile stalwart stationary staunch staying put steadfast steady stout strong sturdy substantial sure together tough unalterable unchangeable unfluctuating uniform unvarying unwavering well-built well-founded

Antonyms: inconstant shaky unfixed unstable wobbly