Unknown. Probably from bellen (“to bark”) with the iterative suffix + -ern. The -f- is explainable either as a phonetic intensification, onomatopoeia, or by influence of other dog-related sound vocabulary (Middle High German baffen, German kläffen); compare also the pair gellen and gelfern, gelfen. Attested since the first half of the 16th century (earliest attestation given below).