In a manner that is abundant, plentiful, or existing in large quantities.
From abounding (present participle of abound) plus the adverb-forming suffix '-ly,' creating an adverb modifying verbs or adjectives.
Adding '-ly' to adjectives is so common we don't notice it, but 'aboundingly' shows how we build adverbs—it's like word-assembly that English speakers understand instinctively.
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