The word 'swampy' is a straightforward English formation. Its core, 'swamp', likely entered English in the early 17th century from a North Germanic source, akin to the Old Norse 'svöppr', meaning 'sponge' or 'fungus'. This original sense of a soft, absorbent substance evolved metaphorically to describe soft, waterlogged ground. The productive English adjectival suffix '-y', with its ancient Proto-Germanic origins, was then appended to create 'swampy', literally meaning 'full of swamp' or 'characterized by swamp-like conditions'.

Structure: swamp (marsh) + y (adjective suffix) swamp (from a Germanic source, meaning 'sponge' or 'fungus', later 'soft, wet ground'); y (from Old English -ig, an adjective-forming suffix meaning 'characterized by' or 'full of').