glass-bottom

The compound "glass-bottom" is a modern descriptive formation, combining two ancient Germanic nouns. "Glass" originates from a Common Germanic root, likely referring to the shiny, transparent substance. "Bottom" stems from a Proto-Germanic word for the ground or foundation. Their union in the 19th or early 20th century was driven by tourism and marine exploration, creating a transparent window in the lower hull of boats. This literal combination of "a bottom made of glass" logically names a feature designed for the practical purpose of underwater observation, transforming a vessel's base into a viewing portal.

Structure: glass (material) + bottom (lower part) - glass: From Old English glæs, of Germanic origin; related to Dutch glas and German Glas. Functions as a noun used attributively to specify the material. - bottom: From Old English botm, of Germanic origin; related to Dutch bodem and German Boden. Functions as a noun specifying the part of an object.