Auburn is reddish brown, and it is said of hair almost exclusively. Between chestnut and copper, catching the light red.
English has a surprisingly precise vocabulary for hair colour, and auburn sits between red and brown, darker than ginger and warmer than plain brown. Novels use it constantly for exactly that reason, since it says more than red would. Oddly, the word once meant whitish or pale yellow, and shifted over centuries towards the colour it names now. It is only ever a colour word, and it takes no other sense at all.
1adjectiveauburnOf a reddish-brown colour, used of hair.
“She had thick auburn hair.”
Auburn used to be blonde. Medieval Latin alburnus meant whitish, from albus, white, and Middle English aubourne was a yellowish white. The word only turned red when English confused it with brun, brown.
Latin
albus — white
Medieval Latin
alburnus — whitish
Old French
auborne
Middle English
aubourne
English, today
auburn
Built from
Early Modern English auburn (“brown, reddish brown”) from Middle English aubourne, abron, abroune, abrune (“light brown, yellowish brown, blond”), alteration (due to conflation with Middle English brun (“brown”)) of earlier auborne (“yellowish-white, flaxen”) from Old French auborne, alborne (“blond, flaxen, off-white”) from Medieval Latin alburnus (“whitish”), from Latin albus (“white”). More at albino, brown.
Etymology from Wiktionary, CC BY-SA