We all new Siri has some jokes, but this one is not what you'd expect from the A.I. who doesn't care for profanity.
When asked the first time, she gives the response which you’d probably expect.
“As a noun it means a woman in relation to a child or children to whom she has given birth,” Siri says.
She will then ask if you’d like to hear the next response. Upon saying yes, she replies, “As a noun it means short for mother****er.”
Source: Newsweek