Without a solid reason or basis; not supported by facts or evidence.
From 'ground' (foundation, basis) plus '-less' (suffix meaning without). 'Ground' itself comes from Old English 'grund,' originally meaning 'bottom' or 'foundation,' used metaphorically for 'basis' by Middle English.
A 'groundless fear' is kind of poetic—it's anxiety without any firm earth under it, just floating in your head. The word combines concrete imagery (ground as solid earth) with abstract meaning (ground as basis), which is why it's survived so well.
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