By 1771, when Tobias Smollett wrote in The Expedition of Humphry Clinker about “An antiquated Abigail, dressed in her lady’s cast clothes”, the term had been around for about a century. It means a lady’s maid.
It had been borrowed from a character in a play by Francis Beaumont and John Fletcher, The Scornful Lady, dated 1616. This had been first performed by the Children of the Queen’s Revels, a troupe of child actors, which was a theatrical convention popular at the time. The play was a comedy of fantastic love and high life in London that became a favourite of audiences in following decades, especially after the Restoration in 1660 Samuel Pepys recorded in his Diary that he saw it no less than five times between 1660 and 1668.
By coach to the King’s playhouse, and there saw “The Scornfull Lady” well acted; Doll Common doing Abigail most excellently, and Knipp the widow very well.
Pepys’s Diary for 27 December 1666.
In the play, Abigail was an alternative name of the maidservant, described as “a waiting gentlewoman” whose real name was Younglove. This implies that the word was even then a generic term applied to a maid. The suggestion is that it was a Biblical allusion, to the first book of Samuel, “And when Abigail saw David, she fell at his feet, and said ‘hear the words of thine handmaid’.” On the other hand, Biblical names were common at the time and it may just have been plucked out of the air.
The rather rare male equivalent was Andrew. In 1698, Congreve refers in his play The Way of the World to “Abigails and Andrews”, a collective term for servants. This mustn’t be confused with merry-andrew, slang for a clown or a mountebank’s assistant at a fair, which also comes from the male forename, though nobody quite knows why.