Why is the ninth month called September?
Old English deah, deag "a color, hue, tinge," perhaps related to deagol "secret, hidden, dark, obscure," from Proto-Germanic *daugilaz (cf. Old Saxon dogol "secret," Old High German tougal "dark, hidden, secret").
Old English deagian "to dye," from the source of dye (n.). Spelling distinction between dye and die was not firm till 19c. "Johnson in his Dictionary, spelled them both die, while Addison, his near contemporary, spelled both dye" [Barnhart]. Related: dyed. Figurative phrase dyed in the wool (or grain) is from dyeing while the material is in its raw state, which has a more durable effect.
A substance used to color materials or substances, such as cells, tissues, and microorganisms.
The art of dyeing is one of great antiquity, although no special mention is made of it in the Old Testament. The Hebrews probably learned it from the Egyptians (see Ex. 26:1; 28:5-8), who brought it to great perfection. In New Testament times Thyatira was famed for its dyers (Acts 16:14). (See COLOUR.)