Without glass; lacking a glass covering, container, or viewing surface.
From 'glass' + the suffix '-less' (meaning without or lacking). This straightforward English construction has been used since at least the 1600s for objects designed without glass components.
Before eyeglasses became widespread in the 1300s-1400s, people were 'glassless' and had to develop other strategies for vision problems—some used pinhole techniques or just accepted blurry sight, which probably shaped how people worked and what jobs they could do.
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