Synonyms For "Firm" :
1 syllable:
fast, hard, house, stiff, strong
2 syllables:
firmly, forceful, healthy, loyal, secure, settled, solid, stable, steadfast, steady, tauten
3 syllables:
immobile, resolute, steadfastly, truehearted
4 syllables:
unbendable, unfaltering, unfluctuating, unshakable, unwavering