Why is the ninth month called September?
c.1300, blenden, "to mix, mingle, stir up a liquid," in northern writers, from or akin to rare Old English blandan "to mix," blondan (Mercian) or Old Norse blanda "to mix," or a combination of the two; from Proto-Germanic *blandan "to mix," which comes via a notion of "to make cloudy" from an extended Germanic form of the PIE root *bhel- (1) "to shine, flash, burn" (see bleach (v.); also blind (adj.)). Cf. Old Saxon and Old High German blantan, Gothic blandan, Middle High German blenden "to mix;" German Blendling "bastard, mongrel," and outside Germanic, Lithuanian blandus "troubled, turbid, thick;" Old Church Slavonic blesti "to go astray." Figurative use from early 14c. Related: Blended; blending.
"mixture formed by blending," 1690s, from blend (v.).