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Webster 1913 Edition

Noun.

One who swerves from and is unfaithful to the marriage vow.

[Poetic]

Shak.

Noun.

[bed and swerve.] One that swerves from his bed; that is one who is false and unfaithful to the marriage vow.

bedswerver ‎(plural bedswervers)

One who is unfaithful to the marriage vow.
- 1623, William Shakespeare, The Winter's Tale, II.i.704-5, 709-10
  I have said / She's an adulteress; I have said with whom... that she's / A bed-swerver, even as bad as those...