Meaning

noun the act of walking with a slow heavy gait

verb walk heavily and firmly, as when weary, or through mud

originFrom Middle English *plodden (found only in derivative plodder), probably originally a splash through water and mud, from plodde, pludde (“a puddle”) (whence modern plud). Compare Scots plod, plodge, plodder, dialectal Dutch plodden, plodderen, dialectal German ploddern, Danish pladder (“mire”).

Etymology from Wiktionary, CC BY-SA 3.0