OED
Postulate: A fundamental principle, presupposition, or condition, esp. one assumed as the basis of a discipline or theory; (also) a proposition that is (or is claimed should be) taken as granted; esp. one (to be) used as a basis for reasoning or discussion, a premise.
A postulate is accepted as true, and it doesn't need to be proven when used as the basis for another argument - it is a fundamental principle and we don't want to be re-inventing the wheel by proving it all over again
OED:
Posit: To put forward or assume as fact or as a basis for argument, to presuppose; to postulate; to affirm the existence of.
A posit, in contrast, is assumed on the basis that it will (hopefully) prove to be true. A possible explanation of how something happened is a posit. If you observe (for example) that economic inflation is occurring, you could posit that increasing wages is driving it, and then set out to collect facts to prove or disprove that posit.
I concur with Bill Franke and J.R. that you want proposal here. But I don't think it's a matter of formal vs informal usage. It seems to me that the core difference between these two words is the depth of consideration and confidence they imply.
You're in a committee meeting wrestling with a problem and a Bright Idea occurs to you. You throw it out on the table for the group to examine and discuss — that's a suggestion. In fact, if you see dubious expressions on some people's faces you may say exactly that — “Just a suggestion, guys,” to indicate that you're not committed to it, you just think it's worth exploring.
Subsequently, the group looks at your suggestion from many angles, considers its possible side-effects, modifies it in some respects to reduce costs, extends it in other respects to increase benefits, and agrees at last that you're not going to come up with anything better. Now you put all your useful thoughts into formal language, carefully craft your exposition to demonstrate the depth and breadth of your examination, frankly admit possible drawbacks to cover your asses, arbitrarily insert passages (of negligible relevance and dubious legitimacy) which will appeal to management's known prejudices, and pass the document upstairs — that's a proposal. In fact, you may entitle it Framistatitude: a Proposal for Indeflature of Ongoing Porsitility.
Mutatis mutandis, that's how a thesis works. You take a Bright Idea — a suggestion — to your advisor, work it up, modify it, contradict it, revise it, massage it, bolster it with a Review of Literature, rewrite repeatedly; and when you're done you present it to your reviewers. At that point you're committed. You must not offer them anything so tentative and vulnerable as a suggestion: that's an invitation to evisceration. It's got to be bold, assertive, confident. It has to be a proposal.
Best Answer
The distinction comes from the two fields of electrical engineering and electronics (which some consider a subset of the former). Electronics refers to technology that works by controlling the motion of electrons in ways that go beyond electrodynamic properties like voltage and current. That is, electrical technology would work the same if you replaced electrons by some other charge-carrying particles, but electronic technology depends on the specific properties of electrons themselves, such as in semiconductor medium.
Because electronic devices are typically used for representing and manipulating information, this makes for a simple rule of thumb for distinguishing electrical and electronic. Typically, if something uses electricity merely as energy, it is electrical, while if it uses electricity as the medium for manipulating information, it is almost surely electronic.