Hereswith combines the Old English here (army) and swith (strong). Hereswith (c. 615-c. 690) was the Northumbrian princess and sister of Saint Hilda of Whitby — queen of the East Angles, later became a nun at Chelles in Gaul.
Featured in Bede's Ecclesiastical History.
Hereswith 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 Hereswith reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.