yodan verb with 'mu' ending (archaic), intransitive verb
turn red; become reddish; become discolored
Archaic intransitive verb. In modern Japanese, 赤くなる or 赤らむ are used instead. The gloss 'rufous' is a technical color term; 'reddish-brown' may be more accessible.
古語では、葉が赤むことを「あかむ」と言った。
In classical Japanese, leaves turning red was expressed as あかむ.
nidan verb (lower class) with 'mu' ending (archaic), transitive verb
Archaic transitive verb. The modern equivalent is 赤める. The cross-reference to 赤める supports this relationship.
See also: 赤める
「赤む」は他動詞としても使われたが、今は「赤める」が一般的だ。
赤む was also used as a transitive verb, but nowadays 赤める is common.
Modern intransitive verb meaning 'to become red' or 'to blush', often used for faces or the sky, replacing the archaic intransitive 赤む.
Derived from 赤 (aka, 'red') + verbal suffix む (mu). The exact historical development is uncertain, but it follows a pattern seen in other color-change verbs.