What is meaning of additional /unlisted list in high court case

In a High Court, an unlisted case is a case that is not listed for hearing on a particular day. A motion list is a schedule of cases that are set to be heard on a given day. Cases that are urgent, left over, or fresh for admission are included in the supplementary list. 

To ensure that urgent cases are heard promptly, lawyers can inform the Registrar of the High Court in writing or by email. The Registrar can then list the case before the appropriate bench.

Accurately explained by expert, and nothing to add.

What is the opinion and advise of the lawyer purposely engaged by you?

Every High Court has its procedure. Your advcate could be instructed to move application for early disposal of the matter.