blatant: [16] Blatant appears to have been coined, or at least introduced, by the poet Edmund Spenser. In the Faerie Queene 1596 he describes how ‘unto themselves they [Envy and Detraction] gotten had a monster which the blatant beast men call, a dreadful fiend of gods and men ydrad [dreaded]’. This ‘blatant beast’ was an allegorical representation of calumny. In the 17th century the word came to be applied to offensively voluble people, but the main modern sense, ‘offensively conspicuous’, does not seem to have developed until the late 19th century.
If the word was Spenser’s own introduction, it is not clear where he got it from. The likeliest candidate seems to be Latin blatīre ‘babble, gossip’, of imitative origin.
blatant (adj.)
1596, in blatant beast, coined by Edmund Spenser in "The Faerie Queen" to describe a thousand-tongued monster representing slander; probably suggested by Latin blatire "to babble." It entered general use 1650s, as "noisy in an offensive and vulgar way;" the sense of "obvious, glaringly conspicuous" is from 1889. Related: Blatantly.