What is another word for sit on or upon?
Pronunciation: [sˈɪt ˈɒn ɔːɹ əpˌɒn] (IPA) 
The phrase "sit on or upon" can be easily replaced with a number of synonyms depending on the context of use. For a casual setting, terms like lounge, recline, sprawl, perch, and nestle could be used to offer a relaxed and comfortable description. Choosing to emphasize the action, terms like rest, prop up, anchor, plant, install, and settle could be utilized. For a more formal context, expressions like take a seat, occupy, assume, be seated, and situate are suitable options. Regardless of the synonym chosen, the meaning remains consistent, and the tone and context are conveyed without any confusion.
