brittle:  Brittle probably comes from a Germanic stem *brut- ‘break’, which had several descendants in Old English (including the verbs brēotan and gebryttan ‘break’) that did not survive the Norman Conquest. It came in a more than usual profusion of spellings in Middle English (bretil, brutil, etc), not all of which may be the same word; brottle, for instance, current from the 14th to the 16th century, may well have come from the aforementioned Old English brēotan. There is also the synonymous brickle , which survived dialectally into the 20th century; this is related ultimately to break.
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" (cognates: Old Norse brjota "to break," Old High German brodi "fragile"), from PIE *bhreu- "to cut, break up" (see bruise (v.)). With -le, suffix forming adjectives with meaning "liable to."