1. periods of time spent seated, especially for a particular activity
Usage: plural form
2. formal meetings or sessions of a court, legislature, or other official body
Usage: formal; legal/political context
3. occasions when someone poses for a portrait or photograph
Usage: art/photography context

Examples

• The portrait required three sittings to complete.
• Parliament held emergency sittings to discuss the crisis.
• The artist scheduled weekly sittings with her model.
• Court sittings were postponed due to the holiday.
• She finished the novel in just two sittings.
• The photographer arranged multiple sittings for the wedding portraits.