"a German," 1833, in modern use, in reference to residents in or natives of German states, sometimes in contrast to Celt; said to be probably a back-formation from Teutonic. Hence 19c. political and newspaper coinages such as Teutomania, Teutophobe, etc.

1610s, "of or pertaining to the ancient Germanic peoples or tribes," from Latin Teutonicus, from Teutones, Teutoni, name of a tribe that inhabited coastal Germany near the mouth of the Elbe and devastated Gaul 113-101 B.C.E.; the name is said to be probably via Celtic from Proto-Germanic *theudanoz, from PIE root *teuta- "tribe" [Watkins].

In linguistics, an old name for the Germanic languages, or for the ancestral speech of the Germanic languages (by 18c.). It later was used in English in anthropology to avoid the modern political association of German. But in this anthropological sense French uses germanique and German uses germanisch, as neither one uses its form of German for the narrower national meaning. Compare French allemand, for which see Alemanni; and German deutsch, under Dutch.

An earlier adjective in English was Teutonie "Germanic" (mid-15c.), from Latin plural Teutoni. The Teutonic Knights (founded late 12c.) were a military order of German knights formed for service in the Holy Land, but who later crusaded in then-pagan Prussia and Lithuania. The Teutonic cross (1882) was the badge of the order.

*teutā-, Proto-Indo-European root meaning "tribe." It forms all or part of: Deutsch; Dutch; Plattdeutsch; Teuton; Teutonic.

It is the hypothetical source of/evidence for its existence is provided by: Old Irish tuoth "people," Old Lithuanian tauta "people," Old Prussian tauto "country," Oscan touto "community," German Deutsch, Gothic þiuda, Old English þeod "people, race, nation," Old English þeodisc "belonging to the people." But Boutkan says it is probably a substratum word.

"a native of Germany," 1520s, from Latin Germanus (adjective and noun, plural Germani), first attested in writings of Julius Caesar, who used Germani to designate a group of tribes in northeastern Gaul, of unknown origin and considered to be neither Latin nor Germanic. Perhaps originally the name of an individual tribe, but Gaulish (Celtic) origins have been proposed, from words perhaps originally meaning "noisy" (compare Old Irish garim "to shout") or "neighbor" (compare Old Irish gair "neighbor"). Middle English had Germayns (plural, late 14c.), but only in the sense "ancient Teuton, member of the Germanic tribes." The earlier English word was Almain (early 14c., via French; see Alemanni) or Dutch. Shakespeare and Marlowe have Almain for "German; a German."

Þe empere passede from þe Grees to þe Frenschemen and to þe Germans, þat beeþ Almayns. [Ranulph Higden’s "Polychronicon," mid-14c., John Trevisa's translation,  1380s]

Their name for themselves, die Deutschen (see Dutch), dates from 12c. Roman writers also used Teutoni as a German tribal name, and writers in Latin after about 875 commonly refer to the German language as teutonicus (see Teutonic). Meaning "the German language" in English is from 1748. High German (1823 in English) and Low German as a division of dialects is geographical: High German (from 16c. established as the literary language) was the German spoken in the upland regions in southern Germany, Low German (often including Dutch, Frisian, Flemish), also called Plattdeutsch was spoken in the regions near the North Sea. In the U.S. German also was used of descendants of settlers from Germany.