Etymology
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butane (n.)
paraffin hydrocarbon, 1875, from butyl, hydrocarbon from butyric acid, a product of fermentation found in rancid butter, from Latin butyrum (see butter (n.)) + chemical suffix -ane.
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buna (n.)

synthetic rubber made from butadiene, 1936, from German Buna, a name chosen by the German Dye Trust, from first elements of butadiene, name of a hydrocarbon (related to butane; the suffix indicates the presence of two double bonds) + Na, indicating sodium (from natrium; see sodium).

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*gwou- 

Proto-Indo-European root meaning "ox, bull, cow," perhaps ultimately imitative of lowing; compare Sumerian gu, Chinese ngu, ngo "ox."

It forms all or part of: beef; Boeotian; Bosphorus; boustrophedon; bovine; bugle; Bucephalus; bucolic; buffalo; bugloss; bulimia; butane; butter; butyl; butyric; cow (n.); cowbell; cowboy; cowlick; cowslip; Euboea; Gurkha; hecatomb; kine.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gaus, Greek bous, Latin bos, Old Irish bo, Latvian guovs, Armenian gaus, Old English cu, German Kuh, Old Norse kyr, Slovak hovado "cow, ox."

In Germanic and Celtic, of females only; in most other languages, of either gender. For "cow" Latin uses bos femina or vacca, a separate word of unknown origin. Other "cow" words sometimes are from roots meaning "horn, horned," such as Lithuanian karvė, Old Church Slavonic krava.

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