Kennedy comes from the Irish surname Ó Cinnéide, meaning "descendant of Cinnéide" — where Cinnéide is from cenn (head) and éide (armour, helmet) — translating roughly as "helmeted head" or "helmeted chief."
John F. Kennedy, the 35th U.S. President, gave the surname its modern resonance.
Kennedy 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.
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In Pythagorean numerology the letters of Kennedy reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.