Wynn is from the Welsh gwyn (fair, blessed, white) — historically a male Welsh name now used as a feminine given name in modern American naming. Saint Wynnfreda — early Welsh saint. Wynn also has Old English roots through the rune Wynn (joy) — one of the runes in the Anglo-Saxon futhorc.
Wynn does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Wynn reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.