Cognomen Blethyn (Blethyn 
) , across the world, is a very rare family name. The family name Blethyn is habitual in Australia, where it is a very rare surname, the United Kingdom, and Israel. Measured by absolute frequency, it most frequently occurs in the United Kingdom, Australia, and the United States. Much less frequently, Blethyn is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Blethyn | Australia, Peru, United Kingdom, United States, Israel |
| david ap blethyn bishop of St Asaph (b. 1250) |
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| william blethyn Bishop of Llandaff, GB (b. 1501) |
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brenda blethyn British actress, GB (b. 1946) |
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| geoff blethyn Australian rules footballer (b. 1950) |
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| william blethyn |
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