Ethel is from the Old English æðele (noble) — a short form of Æthelthryth, Etheldreda, and other Anglo-Saxon names beginning with this element. Ethel Kennedy (1928-2024) — widow of Robert F.
Subject of Robert Massie's Bobby and Ethel (1995).
Ethel 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 Ethel reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.