hypothesis; speculation; conjecture
A formal term for an idea or explanation based on incomplete evidence; often used in academic or intellectual contexts. Similar to 仮説 but with a stronger nuance of personal guesswork.
That theory is still in the realm of speculation.
His claim is nothing more than conjecture.
推測 is a general term for 'guess' or 'inference' and can be used as a verb (推測する). 臆説 is a noun and sounds more formal and abstract.
Standard kanji spelling; 臆 carries the nuance of 'conjecture' or 'guess'.
Variant kanji form; 憶 is also used in words related to memory and thought, but 臆説 is more common.
Compound of 臆 (conjecture, guess) and 説 (theory, explanation). The exact historical derivation is uncertain, but the word follows a common Sino-Japanese pattern for abstract concepts.