Kieffer
A German surname that usually comes from a word for “pine” or “fir,” and in some cases may reflect the trade of a cooper or barrel-maker.
The #5,241 most common surname in the United States (2010 Census) — about 1 in every 46,386 Americans shares it.
Etymology
Kieffer is a German surname associated with the word for resinous conifer wood, especially pine or fir. The historical sources you provided also link it with meanings such as “cooper” in Alsace and with a German word for “jaw,” but the wood-related explanation is the most straightforward surname origin. Because 19th-century surname writers sometimes grouped several similar-looking names together, the exact derivation can vary by family line.
History
The surname appears in German-speaking areas and in Alsace, where German and French naming traditions overlapped. Spelling forms such as Kiefer, Kieffer, and Kiffer occur in historical records, and the name later spread through migration to North America. In modern usage it is found chiefly among descendants of German-speaking immigrants.
Origin
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Fun fact
In German, Kiefer can also mean “jaw,” so older surname explanations sometimes drew on a different meaning than the one most people would expect.
From the historical record
“Keefe. Irish O’Keefe. Or D. Kieffer ; p.n. ; D.B. Chevre ; A.S. ceafor (a beetle) Keel. From Keele ; a loc. n., Staffs”
— British Family Names: their origin and meaning (2nd ed.)