This word is usually used to distinguish it from manolaya (cessation, laya, of the mental movements, vrtti’s of the mind (manas). In manonāśa one knows the status of the mind and is free from it through correct self-knowledge.

In manolaya the mind has become silent as in samādhi. The latter, however, is an experiential state from which one will emerge again. Whether the mind is silent or not, it remains mind. Freedom is being free from regardless of a busy mind or a silent mind, as the silent witness (sākṣī) of that mind, which is also its real substrate.

Manonāśa and manolaya are just words, but are often interpreted in this way in Vedānta to remove misunderstandings about freedom.