only speculation; just guesswork; a matter for conjecture
Used when something cannot be confirmed and remains within the realm of speculation. Often appears in formal or analytical contexts.
The cause is still only speculation.
His motive is just guesswork, but there may have been financial problems.
A set phrase composed of 推測 (speculation), の (possessive particle), 域 (realm/level), を (object marker), and 出ない (does not exit). Literally 'does not leave the realm of speculation'.