Cai
An uncommon surname that may sometimes reflect a Welsh or Cornish name form, but its exact origin is not firmly established from the excerpts provided.
The #4,191 most common surname in the United States (2010 Census) — about 1 in every 36,508 Americans shares it.
Etymology
The excerpts do not give a clear dictionary entry for Cai itself, so the surname’s origin remains uncertain here. In British naming tradition, Cai can be related to the Welsh personal name Cai, a form associated with the legendary Sir Kay; elsewhere, similar short spellings may also arise as reduced or altered forms of other names. Because the evidence supplied is incidental rather than direct, the safest reading is that the surname has an uncertain origin and may reflect a personal-name source rather than a fixed place or trade.
History
The name appears in the historical record as a very rare surname, with only a small number of modern bearers in the United States. Because the excerpts do not provide a direct etymological discussion of Cai, there is no solid basis here for a fuller migration history. In practice, surnames of this shape often survive as localized spellings or as later anglicized forms of older Celtic personal names.
Origin
Regions
Variant spellings
Fun fact
Cai is also the traditional Welsh form of the name associated with Sir Kay, one of Arthur’s knights.
From the historical record
“SHEAFF JSc^a/ya [O.E. jc^a/, a sheaf] 5cAi/ occurs in the A.-Saxon genealogies as the name of a mythical ancestor of Woden ; and Scdafa was the name of a Lombardic king — Sciafa [wfeold] Longbeardum. —”
— Surnames of the United Kingdom: a concise etymological dictionary (2 vols in 1)