Bill Cosby -- Two Accusers Join Defamation Lawsuit

Two women who have previously accused Bill Cosby of sexual assault have joined a third in suing the comedian for defamation ... claiming his alleged lies have ruined their reputations.

As TMZ first reported, Tamara Green sued Cosby claiming he was untruthful when he denied her sexual assault allegations. Green cannot sue for the alleged assault because the statute of limitations ran decades ago, but her lawyer thinks Cosby's denials opened the door to a defamation suit.

Now Green has company ... with Linda Traitz telling CNN she and fellow accuser Therese Serignese are joining Green's lawsuit. Both women claim Cosby drugged them when they were in their late teens.

Traitz has a long criminal past and was released from prison in 2012 after serving more than three years for trafficking Oxycodone, possession of a controlled substance and obtaining a controlled substance by fraud.