Woof

google

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early 19th century: imitative.

wiktionary

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From Middle English oof, owf, from Old English ōwef, āwef, from ō-(“on”) +‎ wef(“web”), from Old English wefan(“to weave”), from Proto-Germanic *webaną(“to weave”), from Proto-Indo-European *webʰ-, *wobʰ-(“to weave, to lace together”).

Onomatopoeic. 

woof

etymonline

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woof (n.1)

"weft, texture, fabric," Old English owef, from o- "on" + wefan "to weave" (see weave). With unetymological w- by influence of warp or weft.

woof (n.2)

dog bark noise, 1804, echoic.