urbane (adj.)

"of the same parents or grandparents," c. 1300, from Old French germain "own, full; born of the same mother and father; closely related" (12c.), from Latin germanus "full, own (of brothers and sisters); one's own brother; genuine, real, actual, true," related to germen (genitive germinis) "sprout, bud," which is of uncertain origin; perhaps it is a dissimilation of PIE *gen(e)-men-, suffixed form of root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.

Your cousin-german (also first cousin) is the son or daughter of an uncle or aunt; your children and your first cousins are second cousins to one another; to you, your first cousin's children are first cousins once removed.

mid-14c., "having the same parents," a doublet of german (adj.) but directly from Latin germanus instead of via French (compare urbane/urban). 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 loosened sense of "closely related, akin" (late 15c.) in reference to things, not persons.