woodyoudaoicibaDictYouDict[wood 词源字典]
wood: [OE] The ancestral meaning of wood is probably ‘collection of trees, forest’; ‘tree’ (now obsolete) and ‘substance from which trees are made’ are secondary developments. The word goes back to prehistoric Germanic *widuz, which also produced Swedish and Danish ved ‘firewood’, and it has Celtic relatives in Gaelic fiodh ‘wood, woods’, Welsh gwydd ‘trees’, and Breton gwez ‘trees’.

Its ultimate source is not known for certain, although it has been suggested that it may go back to the Indo- European base *weidh- ‘separate’ (source also of English divide and widow). According to this theory, it would originally have denoted a ‘separated’ or ‘remote’ piece of territory, near the outer edge or borders of known land; and since such remote, uninhabited areas were usually wooded, it came to denote ‘forest’ (forest itself may mean etymologically ‘outside area’, and the Old Norse word for ‘forest’, mork, originally signified ‘border area’).

[wood etymology, wood origin, 英语词源]
wood (n.)youdaoicibaDictYouDict
Old English wudu, earlier widu "tree, trees collectively, forest, grove; the substance of which trees are made," from Proto-Germanic *widu- (cognates: Old Norse viðr, Danish and Swedish ved "tree, wood," Old High German witu "wood"), from PIE *widhu- "tree, wood" (cognates: Welsh gwydd "trees," Gaelic fiodh- "wood, timber," Old Irish fid "tree, wood"). Out of the woods "safe" is from 1792.
wood (adj.)youdaoicibaDictYouDict
"violently insane" (now obsolete), from Old English wod "mad, frenzied," from Proto-Germanic *woda- (cognates: Gothic woþs "possessed, mad," Old High German wuot "mad, madness," German wut "rage, fury"), from PIE *wet- (1) "to blow; inspire, spiritually arouse;" source of Latin vates "seer, poet," Old Irish faith "poet;" "with a common element of mental excitement" [Buck]. Compare Old English woþ "sound, melody, song," Old Norse oðr "poetry," and the god-name Odin.