answer a philosophical / historical question

"Great Philosophers" is a somewhat nebulous term and can be researched using Google.
Your question is covered by a large body of work termed "Philosophy of Mind". There are thousands of papers published on the subject.
But simplistically, philosophers tend to gravitate towards two poles on this.
1. The idealists who argue that there are only mental phenomena.
2. The reductionist/ materialists who argue that mental events can be reduced to physical processes.
In the middle ground you have the Cartesian dualists who argue that mental events and physical events are separate realms with no clear means of connection.
In addition there is the fundamental point that the word is in your question "What is thought" is itself a problematic concept (a product of thought), which some philosophers have tried to eliminate by use of a verb named "E-prime". Language has tended to replace mind as the focus for philosophy since the advent of psychology in the 20th. century.

I should perhaps have added that if you do delve further into these issues you will find that your original question tends to dissipate when an ontological level of analysis is reached. (i.e. what does is-ness mean, or what does it mean to be anything).

I don't know about the great philos, Guy, but to your Average Clod (me) thought is merely the circulation of electrons (and/or other charged particles) constituting certain consistent patterns in the brain or computer chip

Nature works with a code, a set of rules, if you take mind out of the reasoning on the nature of reality, your position is barely distinguishable from the reductionists. Materialism is not a requisite in my arguments on the subject. The problem is you have done much more then asserting just this. You have tried to "explain" what is the proper place of language which is via/through minds without sufficiently justifying why "language" is not in nature at large itself. You speak of active mind process like "construction" to frame the scope of languaging. I personally don't see any difference from DNA code and linguistics. I also have a very poor idea on what "mind" means to convey. It is for all know purposes an obscure term.
Rules and exchange of information are more fit terms to explain language then Consciousness will ever be.

Where do you stand on the particular issues you mentioned Fresco?

(The next paragraph above is more important for understanding my own viewpoint)

If I take a stand at all, I follow Wittgenstein in the view that all words including "thought" take their meaning from the context of their usage. Sometimes "thought" implies an ongoing process...sometimes a single concept...sometimes a mental event associated with a neural event...etc.
Thus the original question "what is thought" has been transcended in an investigation of the role of language in human interactions with each other and what they call "the world". On this, I tend to take a "systems approach" (following Maturana) which involves nested levels of analysis from the biological to the social.

Just checking in.

i can play guitar but cannot define guitar playing.

thought is cognition.
cognition is process of mind