sign up verb 4/ˈsaɪnˌʌp/ noun 1forms 4 verb4 •To add a name to the list of people who are participating in something.We signed Bob up for kitchen cleanup duty. •To add one's own name to the list of people who are participating in something (including amateur, but not professional, teams).Terry signed up for the soccer team. •To enlist in the armed forces.Didn't you hear? He's just signed up! •To agree to purchase some good or service.After much deliberation we decided to sign up for satellite TV. sign-up /ˈsaɪnˌʌp/ noun1 •The act of signing up, as for a commercial service or a committee. formssigned up · signing up · signs up · sign-ups