Threatening, as of weather conditions; ominous: surly clouds filled the sky.
Obsolete Arrogant; domineering.
[Middle English sirly, masterful, lordly, from sir, lord; see sir.] sur'li·ly adv., sur'li·ness n.
Word History: That the word surly means "churlish" nicely indicates its fall in status. Churlish derives from the word churl, which in its Old English form ceorl meant "a man without rank, a member of the lowest rank of freemen," as well as "peasant." In Old English ceorl may have been a term of contempt; it certainly became one in Middle English, where cherl meant "base fellow, boor," with churlish descending in meaning accordingly. Surly, on the other hand, started life at the top of the scale. In Middle English and Early Modern English, surly was only one spelling for this word; another, sirly, reflects its origin in sir, the term of honor for a knight or for a person of rank or importance. Sirly, the form under which the early spellings of the word are entered in the Oxford English Dictionary, first meant "lordly." Surly, entered as a separate word in the OED and first recorded in 1566, meant perhaps "lordly, majestic," in its earliest use and was subsequently used in the sense "masterful, imperious, arrogant." As the gloss "arrogant" makes clear, the word surly could have a negative sense, and it is this area of meaning that is responsible for the current "churlish" sense of the word.
[sur-lee] 
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