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"Teuton, member of the Germanic tribes," 1520s (plural Germayns attested from late 14c.), from Latin Germanus, first attested in writings of Julius Caesar, who used Germani to designate a group of tribes in northeastern Gaul, origin unknown, probably the name of an individual tribe. It is perhaps of Gaulish (Celtic) origin, perhaps originally meaning "noisy" (cf. Old Irish garim "to shout") or "neighbor" (cf. Old Irish gair "neighbor"). The earlier English word was Almain (early 14c.) or Dutch.

Þe empere passede from þe Grees to þe Frenschemen and to þe Germans, þat beeþ Almayns. [John of Trevisa, translation of Higdon's Polychronicon, 1387]

Their name for themselves was the root word of modern German Deutsch (see Dutch). Roman writers also used Teutoni as a German tribal name, and Latin writers after about 875 commonly refer to the German language as teutonicus. See also Alemanni and Teutonic. As an adjective, from 1550s. The German shepherd (dog) (1922) translates German deutscher Schäferhund. German Ocean as an old name for the North Sea translates Ptolemy. German measles attested by 1856.

germane (adj.) mid-14c., "having the same parents," derived from german (adj.); cf. human/humane, urban/urbane. Main modern sense of "closely connected, relevant" (c.1600) derives from use in "Hamlet" Act V, Scene ii: "The phrase would bee more Germaine to the matter: If we could carry Cannon by our sides," which is a figurative use of the word in the now-obsolete sense of "closely related, akin" (late 15c.) in reference to things, not persons.