An Etymological Dictionary of the German Language/Annotated/Kiefer
Kiefer (1.), masculine, from the equivalent Middle High German kiver (masculine, neuter ?), kivel, kivele, ‘jaw, jawbone,’ besides which there is a form from the stem of kauen, Middle High German kiuwel, masculine, and usually kiuwe, këwe, feminine, ‘jaw, jawbone.’ Yet Modern High German kiver, kivel, have, notwithstanding their rare occurrence, a remoter history in the past; with Gothic *kifru- is connected Old Icelandic kjǫptr, kjaptr (Gothic *kiftus), ‘mouth (of beasts), jawbone,’ and also with the a stage of gradation, Anglo-Saxon ceafl, Old Saxon kafl, masculine, ‘jaw of animals’ (with regard to the gradation compare Käfer, Giebel, and Kerl). The Teutonic stem is therefore kef, kaf, or rather keb, kab (before l and r later permutations of b to f sometimes occur), from pre-Teutonic geph or gebh; compare Zend zafare, zafra, neuter, ‘mouth, jaws’ (the corresponding term in Sanscrit *japhra, *jabhra, is wanting); the nasalised root jambh, by gradation jabh, ‘to snap at,’ leads to Greek γαμφαΐ, γαμφηλαί, ‘jaws,’ yet these are probably connected more closely with the cognates discussed under Kamm. See Käfer.
Kiefer (2.), feminine, ‘pine,’ early Modern High German only; it cannot be traced further back; in Upper German Föhre simply. Hence Kiefer probably originated in Kienföhre (respecting the obscuration of old compounds compare Wimper, Schultz, and Schuster). The intermediate form kimfer is recorded as North Bohemian. Compare also Middle High German kienboum, masculine, ‘pine,’ and *kienforhe, feminine, ‘pine-tree’ (attested by the derivative kienforhîn, adjective, ‘of pine’). Compare Kien and Föhre.