donkey – осел

donkey (n.) (сленговое, вероятно уменьшительное от «dun» - скучный серо-коричневый)
1785, originally slang, perhaps a diminutive from dun "dull gray-brown," the form perhaps influenced by monkey. Or possibly from a familiar form of Duncan (compare dobbin). The older English word was ass (n.1).

1888:
The stem is dun, a familiar name for a horse, as used in the common phrase ' dun is in the mire ; ' as to which see Chaucer, C. T. Mancip. Prol. 1. 5 ; Shak. Romeo, i. 4. 41. The name dun was given to a horse or ass in allusion to its colour ; see Dun. Similarly was formed dunnock, M. E. donelt, a hedge-sparrow, with a single suffix -ock.
Корень – «dun», грубоватое прозвище лошади; дано лошади или ослу по асcоциации с цветом.

DUN – серо-коричневатый цвет, мышиный.

Т.е. цвет дыма. Наше слово – «дымка». Кличка, обычно, «Дымок». Замена «м» - «n». ДМК – DMK – DNK – donkey.