Old English bread "bit, crumb, morsel; bread," cognate with Old Norse brauð, Danish brød, Old Frisian brad, Middle Dutch brot, Dutch brood, German Brot. According to one theory [Watkins, etc.] from Proto-Germanic *brautham, which would be from the root of brew (v.) and refer to the leavening.
But OED argues at some length for the basic sense being not "cooked food" but "piece of food," and the Old English word deriving from a Proto-Germanic *braudsmon- "fragments, bits" (cf. Old High German brosma "crumb," Old English breotan "to break in pieces") and being related to the root of