As hard as iron; extremely hard. rare before 19th cent.

In proverbial similes, as dry as (a) bone, hard as (a) bone, white as (a) bone, etc. Cf. compounds 4.

Made, or having the qualities, of adamant (adamant, n. 1a); unable to be broken or dissolved; unbreakable; impenetrable. Also figurative and in…

Resembling stone in consistence; hard like stone; very hard.

Chiefly poetic. Made or consisting of adamant. Also figurative (cf. sense A. 1b). Cf. adamantine, adj. 1a.

With the sense ‘resembling steel’ (in colour, hardness, etc.), as steel gloss; steel-bright, steel-hard, steel-sharp, steel-straight, steel-strong…

buff accoutrements, belt; buff-hide, buff-skin; †buff-hard adj.

Resembling steel in appearance, colour, hardness, or some other quality.

Hard as diamond, adamantine. Obsolete.

figurative. = as hard as steel, steely.

Rocky, stony; (in later use) spec. covered in rocks. rare before 19th cent.

Taken as the type of hardness (whence formerly turned into bowls for bowling): thence the simile as hard as brazil still common dialectally, and…

Having the hardness or strength of adamant; = adamantine, adj. 1a.

That resembles bone in hardness or firmness.

Of an object, substance, etc.: extremely hard or strong.

As hard as iron; iron-like. Also figurative. Cf. ferrean, adj. rare.

Of an object: resembling a rock in appearance or physical characteristics.

figurative. Hard, insensible to fatigue; rigid, stern, unbending; ‘hard-and-fast’, unyielding, wanting in pliancy or adaptiveness. (Hyphenated.)

Similative, as bone-grey, bone-hard, etc. Cf. phrases 2.