To a very great degree; extremely. It can also mean in a way that is hard to believe.
From 'incredible' plus the adverb-forming suffix '-ly'. It keeps the original sense of ‘beyond belief’ while serving as a general intensifier.
In everyday speech, 'incredibly' often just means ‘very’, but it still hints at ‘almost too much to believe’. That tiny flavor of exaggeration is what makes it feel stronger than plain ‘very’.
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