Without a beam; lacking beams or light, or not smiling or radiant.
From 'beam' plus the suffix '-less' (meaning 'without'), a common English pattern for creating adjectives that negate or indicate absence of a quality.
The '-less' suffix is one of the most productive in English—you can add it to almost any noun and create a new word instantly. 'Beamless' shows how this ancient suffix (from Old English) still lets us invent words speakers instantly understand.
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