As in a duel, the second could step in to cover for the leading man, but otherwise played a strong supporting role. In every line of business for which two or more actors were employed, the second deferred to the principal. A stock company might include a second heavy, a second low comedian, a second old man, and (perhaps doubling as a low comedienne) a second old woman. According to Gladys Hurlbut in Next Week-East Lynne!, "the thing to look for when you hired second people was a slight case of menace. If a man suggested betrayal more than rescue, he was a second man type, and if a girl was too tall for soubrettes and you could picture her as a correspondent, then she was a second woman. . . . Second people were often very good actors and popular too. . . . The second woman got some fat parts but not too many. She played the rough comedy leads, like the Florence Moore farces that were too naughty for the little leading lady, and I had to fight to get Craig's Wife away from the second woman because the management thought it would hurt my popularity to be so mean all week" (1950, 154-55).
The Historical Dictionary of the American Theater. James Fisher.