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Synonyms for Abysmal (same or very similar meaning)

WordNet sense 1 (impossible to measure):
immeasurable, immensurable, unmeasurable

WordNet sense 2 (so deep as to be unmeasurable):
abyssal, unfathomable

WordNet sense 3 (having great spatial extension or penetration downward or inward from an outer surface or backward or laterally or outward from a center; sometimes used in combination):

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