Thunk is to think together, or alone. To create inside your head, without formalising these thoughts into a concrete written proposal. It is the first part of a creative process.
It is not the same as thinking, which is a creative roaming over topics. It is a gestational activity, sometimes obsessive, in which an idea is mulled over for days or months before it takes concrete form.
On occasion a thunk is very concrete. It can be elaborated verbally in detail. However until it is written down, or recorded it is a free agent. There is no authorship, or copyright associated with such an act. Thunking is as such a shared act. A gift.
A thunk becomes a creative proposition when it is written down or recorded. It is at that time that considerations such as copyright, and intellectual property come into force. This is a small difference in the realm of ideas, indeed there may be no difference in the content or refinement between a Creative Proposition and a thunk, but it is all the difference in the world of the relations between people.
Accreditation is important. And with thunking it is polite to give it as such - see credits at the bottom of Bar Dapp White Paper.