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She understood the concept fully.
She understood the concept completely.
to the greatest extent or degree; completely
He was fully prepared for the exam.
He was completely ready for the exam.
The room was fully decorated for the party.
The room was entirely decorated for the party.
Often used to emphasize completeness or totality.
'Fully' is often used to describe something that is complete or to the maximum extent.
'Fully' is an adverb and should not be used as an adjective.
From Middle English 'fulliche', from Old English 'full' (full) + '-lice' (adverb suffix).
Can be used as an adverb to emphasize that something is done to the maximum extent possible.