Williamina is the feminine of William. Williamina Fleming (1857-1911) was the Scottish-American astronomer at Harvard College Observatory who began work as Edward Pickering's housekeeper and ended up director of the team of women known as the "Harvard Computers." She personally classified over 10,000 stars and discovered the Horsehead Nebula (1888).
Featured in Dava Sobel's The Glass Universe (2016).
Williamina 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 Williamina reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.