A person or thing has either not made a debut, is making a debut, or has already made a debut.... there is no opposite.
Sonakshi Sinha debuted in Dabangg. She won the award for best debut that year. Salman Khan was there in the opposite role.
Neelam Kothari
Badlands
Perhaps you are thinking "unreleased" as in an song or video that has not been made public or has not debuted.
Saawariya was Ranbir Kapoor's debut film. He performed opposite to Sonam Kapoor. The movie was released with Om Shanti Om.
Parampara is Saif Ali Khan's debut film. He was not a trained actor back then. His recent movie was Cocktail opposite to Deepika Padukone.
Deepika Padukone - Om Shanti Om
Debut comes from France!
debut
Aishwarya Rai made her movie debut in Mani Ratnam's Tamil film Iruvar (1997) opposite Mohanlal.
The Debut was created in 2001.
debut-beginning