I haven’t seen bhante @sujato talk about this from the Upanishads, so I’m tagging it here.
We can find a hierarchical comparison of these in Chāndogya Upanishad, which gives a kind of a gloss for these terms:
7.3.1 — Mano is greater than vaco.
The mind is superior to speech. Just as a person can hold in his fist two āmalaka fruits, or two kola fruits [plums], or two akṣa fruits, so also the mind can hold within it both speech and name. If a person thinks, ‘I will read the mantras,’ he reads them. If he thinks, ‘I will do this,’ he does it. If he decides, ‘I will have children and animals,’ he can try to have them. If he decides, ‘I will conquer this world and the next,’ he can try to do it. [This is the characteristic of the mind. If it says it will do something, it can do it.] The mind is the self. The mind is the world. The mind is Brahman. Worship the mind.
7.4.1 — Saṃkalpa is greater than manas.
The will is certainly superior to the mind. When a person wills, he starts thinking. Then he directs the organ of speech, and finally he makes the organ of speech utter the name. All the mantras merge in the names and all the actions merge in the mantras.
7.5.1 — Citta is greater than saṃkalpa.
Intelligence is certainly superior to will-power. A person first comprehends, and then he wills. Next he thinks it over again and again, and then he directs the organ of speech. Finally he makes the organ of speech utter the name. All the mantras then merge in the names, and all the actions merge in the mantras.
7.6.1 — Dhyāna is greater than citta.
Meditation is certainly superior to intelligence. The earth seems to be meditating. The space between the earth and heaven seems to be meditating. So also, heaven seems to be meditating. Water seems to be meditating. The mountains seem to be meditating. Gods and human beings also seem to be meditating.
7.7.1 — Vijñāna is greater than dhyāna.
Vijñāna [the practical application of knowledge] is certainly superior to meditation. Through vijñāna one knows the Ṛg Veda, the Yajur Veda, the Sāma Veda, and the fourth—the Atharva Veda; then the fifth—history and the Purāṇas; also, grammar, funeral rites, mathematics, the science of omens, the science of underground resources, logic, moral science, astrology, Vedic knowledge, the science of the elements, archery, astronomy, the science relating to snakes, plus music, dance, and other fine arts; also heaven and earth; air, space, water, and fire; the gods and human beings; cattle and birds; creepers and big trees; animals of prey as well as worms, fleas, and ants; merit and demerit; truth and untruth; good and evil; the pleasant and the unpleasant; food and water; and this world and the other world. One knows all this through vijñāna. Worship vijñāna.
Now, ChU’s dating is not certain, and while it might’ve existed in some fashion before Buddhism, some verses may be later.
That being said, there’s a clear hierarchical treatment of these items in the Indic thought of these times. So, it’s reasonable to assume that the Buddha’s audience would have differentiated these terms.
Directly relevant to the Agamas is the MN148, where mano is the interior sense-base, and the corresponding awareness of (mano-)viññana.
MN 133, MN 138, SN 35.97, SN 40.9, SN 22.7 are useful breadcrumbs for an interested party to analyse how these terms appear side by side in differing contexts.
One can map out the context thus more clearly, something I don’t have time for at the moment. 