Dirty or unclean, covered with dirt or stains; or morally corrupt or dishonest.
From 'grub' meaning a larva or maggot (from Old English roots suggesting digging), with the diminutive suffix '-y.' Because grubs are associated with dirt and decay, 'grubby' came to mean 'dirty.' Extended to mean morally unclean by the 1800s.
The word beautifully evolved from literal grubs (the gross larvae) to meaning anything dirty—and then extended to morally 'dirty' situations, showing how our brain links physical disgust with ethical disgust!
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