Old English grundleas "bottomless, unfathomable, vast;" see ground (n.) + -less. Figurative sense of "having no adequate cause or reason" is from 1620s. Similar formation in Dutch grondeloos, German grundlos, Old Norse grunnlauss. Related: Groundlessly; groundlessness.
the allegations proved groundless
ground-breaking
grounded
grounder
ground-hog
grounding
groundless
groundling
grounds
ground-swell
groundwater
groundwork
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