O.E. berstan "break suddenly" (class III strong verb; past tense bærst, pp. borsten), from a W.Gmc. metathesis of P.Gmc. *brestanan (cf. O.Fris. bersta, M.Du. berstan, Low Ger. barsten), from PIE base *bhres- "to burst, break, crack." The forms reverted to brest- in M.E. from influence of O.N. brestan/brast/brosten from the same Gmc. root, but it was re-metathesized late 16c. and emerged in the modern form, though brast was common as p.t. through 17c. and survives in dialect.