An irrational fear of darkness or of being in a dark place.
From Greek 'achlous' (darkness) + 'phobos' (fear). The term appeared in psychological literature in the early 1900s as clinicians began cataloging specific phobias.
Achluophobia is actually rooted in ancient human survival instincts—our ancestors genuinely were vulnerable in darkness—so this fear is less irrational and more 'evolutionarily overactive'!
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