Nouns

(n)firm, house, business firmthe members of a business organization that owns or operates one or more establishments“he worked for a brokerage house”

Verbs

(v)tauten, firmbecome taut or tauter“Your muscles will firm when you exercise regularly”, “the rope tautened”
(v)tauten, firmmake taut or tauter“tauten a rope”

Adjectives

(s)firm, steadfast, steady, stiff, unbendable, unfaltering, unshakable, unwaveringmarked by firm determination or resolution; not shakable“firm convictions”, “a firm mouth”, “steadfast resolve”, “a man of unbendable perseverance”, “unwavering loyalty”
(s)firm, solidnot soft or yielding to pressure“a firm mattress”, “the snow was firm underfoot”, “solid ground”
(s)firm, strongstrong and sure“a firm grasp”, “gave a strong pull on the rope”
(s)firmnot subject to revision or change“a firm contract”, “a firm offer”
(s)firm(of especially a person's physical features) not shaking or trembling“his voice was firm and confident”, “a firm step”
(s)firm, steady, unfluctuatingnot liable to fluctuate or especially to fall“stocks are still firm”
(s)firmsecurely established“holds a firm position as the country's leading poet”
(s)firmpossessing the tone and resiliency of healthy tissue“firm muscles”
(s)fast, firm, immobilesecurely fixed in place“the post was still firm after being hit by the car”
(s)firm, loyal, truehearted, fastunwavering in devotion to friend or vow or cause“a firm ally”, “loyal supporters”, “the true-hearted soldier … of Tippecanoe” (Campaign song for William Henry Harrison), “fast friends”

Adverbs

(r)firm, firmly, steadfastly, unwaveringlywith resolute determination“we firmly believed it”, “you must stand firm”