private plan; one's own plan
A plan or proposal that is personal and not yet official. Often contrasted with a formal or organizational plan.
The manager presented his own private plan at the meeting.
This is just my own plan, but I've thought about next month's event.
He presented his personal proposal at the meeting.
He put together his private plan over the weekend.
She submitted the reform proposal as her own private plan.
腹案 is a plan someone is keeping privately in their mind without announcing it, while 私案 is usually written or presented, even if informally.
私案 (personal, unofficial plan) and 試案 (a tentative draft proposed for testing or discussion) share the same reading しあん but differ in whose plan it is and its purpose.
Compound of 私 (private, personal) and 案 (plan, proposal).