An archaic or obsolete third-person singular present tense form of 'blue,' meaning 'it blues' or 'makes blue' (rarely used in modern English).
From blue (Old English blew) plus the archaic third-person singular suffix -eth (Old English -eth, equivalent to modern -s). This represents Middle English or Early Modern English grammar.
Words ending in '-eth' like 'blueth' are instantly recognizable as archaic because they're how Shakespeare and the King James Bible conjugated verbs—English grammar has simplified dramatically since then!
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