Meaning

adjective without any attempt at concealment; completely obvious

adjective conspicuously and offensively loud; given to vehement outcry

originCoined by Edmund Spenser in 1596 in "blatant beast". Probably a variation of *blatand (Scots blaitand (“bleating”)), present participle of blate, a variation of bleat, equivalent to blate + -ant. See bleat. In addition, it is suggested by Latin blatiō (“speak like a fool, prate”), which is rare, and so the similitude may be just coincidental. Compare typologically Bulgarian вопиющ (vopijušt),…

Etymology from Wiktionary, CC BY-SA 3.0