bog: [13] Bog is of Gaelic origin. It comes from bogach ‘bog’, which was a derivative of the adjective bog ‘soft’. A possible link between Gaelic bog and Old English būgan ‘bend’ (source of modern English bow) has been suggested. The British slang use ‘lavatory’, which dates from the 18th century, appears to be short for the slightly earlier bog-house, which may have been an alteration of the 16th-century boggard – quite possibly completely unrelated to bog ‘swamp’.
c. 1500, from Gaelic and Irish bogach "bog," from adjective bog "soft, moist," from PIE *bhugh-, from root *bheugh- "to bend" (see bow (v.)). Bog-trotter applied to the wild Irish from 1670s.
