"to wander about aimlessly," 1746, earlier "to mumble, grumble" (1620s), both senses perhaps (with a notion of "to speak with a beggar's whine or grumble") from frequentative of maund "to beg" (1560s), which is possibly from French mendier "to beg," from Latin mendicare "to beg, ask alms" (see mendicant).
"Though the etymology of maunder is uncertain, it is clear that it is not a corruption of meander" [Fowler], but the two words seem to have influenced each other. Meaning "to wander in talking like one drunken or foolish" is by 1831. Fowler writes that maunder is "best confined to speech, & suggests futility rather than digression ... & failure to reach an end rather than loitering on the way to it." Related: Maundered; maundering.