Can the calendar entries in Nokia N8-00 and T7-00 be defined as private?

You can create separate calendars for work and free time. The entries from the free time calendar are not synchronised to your work calendar and are therefore not visible e.g. when viewing your work calendar online.

The entries in the work calendar are by default synchronised as public entries. In Symbian Anna (and later) there is an option to define a calendar entry also as a private entry (an entry which is synchronised but hidden from the online viewers).