Meaning

noun a wooden or plastic board on which dough is kneaded or bread is sliced

originFrom bread + board. Regarding definition 3: the etymology is either that electric circuits used to be prototyped on actual bread boards (definition 1) populated with nails, or that solder breadboards have lots of holes and are usually brown (they visually resemble a slice of bread), or a merging of the two. The etymology is less obvious today given the popularity of solderless breadboards.

Etymology from Wiktionary, CC BY-SA 3.0