Definition of "err"

err¹

/ɜː(ɹ)/

verb
third-person singular simple present errs, present participle erring, simple past and past participle erred
1. (intransitive, formal) To make a mistake.
  Quotations
  Artificial tests, then, can hardly err on the side of supplying too many opportunities for one bird to see another perform the act which is the model.
  1910, James P. Porter, chapter 2, in Intelligence and Imitation in Birds; A Criterion of Imitation‎, page 7
2. (intransitive) To sin.
3. (archaic) to stray.

err²

interjection
1. Elongated form of er (“sound of hesitation”).