Is it farther or further?
late 14c., britel, perhaps from an unrecorded Old English adjective *brytel, related to brytan "to crush, pound, to break to pieces," from Proto-Germanic stem *brutila- "brittle," from *breutan "to break up" (cf. Old Norse brjota "to break," Old High German brodi "fragile"), and related to bruise (v.). With -le, suffix forming adjectives with meaning "liable to."
Having a tendency to break when subject to high stress. Brittle materials have undergone very little strain when they reach their elastic limit, and tend to break at that limit. Compare ductile.