sour (adj.) Look up sour at Dictionary.com
Old English sur, from Proto-Germanic *suraz (cf. Old Norse surr, Middle Dutch suur, Dutch zuur, Old High German sur, German Sauer), from PIE root *suro- "sour, salty, bitter" (cf. Old Church Slavonic syru, Russian syroi "moist, raw;" Lithuanian suras "salty," suris "cheese"). French sur "sour, tart" (12c.) is a Germanic loan-word. The verb is attested from c.1300. Sense in whisky sour is from 1885. Sour cream is attested from 1855.