IPA: /prəˈpɒzɪtəs/
KK: /prəˈpɒzɪtəs/
A person who is directly involved in or affected by a particular situation or action.
In the legal case, the propositus was called to testify about the events that took place.
Propositus is derived from "pro-" (meaning for or in favor of) and "ponere" (meaning to place or put). The word refers to something that is put forward or proposed.
Think of something that is 'put forward' ('ponere') for consideration, as 'pro-' means for or in favor of.
No commonly confused words.