Original: E. Cobham Brewer, Dictionary of Phrase and Fable 1898, s.v. "Kissing under the mistletoe" relates the custom to the death of Baldr, without authority.
Simplified: E. Cobham Brewer, Dictionary of Phrase and Fable 1898, s.v. "Kissing under the mistletoe" relates the custom to the death of Balder, without authority.