In a way that is very strong, intense, or impossible to resist; with crushing force or effect.
From 'overwhelm' (over- + whelm, from Old English 'hwelfan' meaning to turn over or capsize) plus the adverbial suffix -ly. It originally meant literally to engulf or submerge, then evolved to mean to overcome emotionally or mentally.
The word literally comes from the image of waves capsizing a boat—and your brain actually feels 'capsized' by emotion or information when you're overwhelmed, because stress hormones really do flood your system and impair decision-making!
Complete word intelligence in one call. Free tier — 50 lookups/day.