I did some personal research on samādhi and jhāna recently and began to summarize what I found (not for future publication, but just to clarify it in my own mind). One of the questions I posed was “What is samādhi, according to the early discourses?” I hope it’s not too presumptuous of me to post this longish excerpt, but I thought it might be pertinent here:
Samādhi
The Pāli word samādhi is composed of sam- (together); ā- (toward); and -dhi (to put or place), giving it the meaning of “putting together”, “collecting”, or “gathering”. It implies a collectedness of mind, a gathering of attention.
In MN 44 (at MN I, 301) the lay follower Visākha asks the bhikkhunī Dhammadinnā, “What is samādhi?” She answers by saying that samādhi is cittassa ekaggatā. Cittassa is straightforward, meaning “of the mind”. Ekaggatā can be broken into its component parts: eka- (one, single); agga- (peak, meeting place, point of convergence); and tā, a suffix meaning “-ness”. So ekaggatā is often translated as “one-pointedness” or “unification”.
This has often been interpreted to mean a fixed, unwavering attention on a single object, free from thought or mental explorations. Bucknell (2019, p. 398), referring to ekaggatā, states: “’(Mental) one-pointedness’ implies absence of thinking”. Anālayo (2014, p. 79) suggests that “conceptual thought” would be “somewhat in contrast to the … quality of mental unification”, also in reference to ekaggatā.
However, in AN 5.151 at AN III, 175 the Buddha lists five recommended qualities one should have when listening to the Dhamma, the fourth of which is ekaggacitto. As it would be difficult to comprehend a Dhamma discourse without conceptual thought, this seems to indicate that the mental unification denoted by cittekaggatā or ekaggacitto instead implies that one’s whole mind, including attention and conceptual thoughts, is fully engrossed in a particular subject.
Further support for this interpretation can be found in the Theravāda Vinaya, where ekaggacittā is used to describe how monastics should listen to the recitation of the Pāṭimokkha—with full attention, with undistracted minds (Mv.II.3.5). Again, conceptual thought would be necessary for understanding the meaning of the reciter’s words.
Thus, it seems likely that samādhi, and by extension cittassa ekaggatā, refers to an undistracted, unscattered mind, one whose thoughts and explorations are only concerned with the matter at hand.
Sammā Samādhi
In the context of the eightfold path, samādhi is distinguished further as sammā samādhi, or “right” samādhi (i.e., the right kind of samādhi for progress toward awakening). Although sammā samādhi is widely equated with the four jhānas in many modern Buddhist circles, Venerable Anālayo (2019) has pointed out that defining them this way appears in only four discourses of the Pāli Canon (DN 22, MN 141, SN 45.8, and AN 5.28). The majority of these discourses lack parallels, thus weakening the assertion that early Buddhism defined sammā samādhi exclusively as the four jhānas.
Several discourses instead define sammā samādhi as unification of mind (cittassa ekaggatā) integrated with the other seven aspects of the eightfold path, with no mention of jhāna (DN 18, MN 117, SN 45.28, and AN 7.42). This definition also further supports a broader interpretation of citassa ekaggatā as meaning “undistracted mind” rather than implying a fixed, immobile attention free from any thought. However, two of these discourses lack parallels, making it more difficult to be certain that this definition is what the Buddha meant by “right samādhi”.
The Samādhi Indriya
The discourses also define samādhi in discussions of the five indriyā, qualities or abilities required for successful practice of the path, of which samādhi is one. SN 48.8 (at SN V, 196), while not explicitly equating the indriya of samādhi with the four jhānas, states that this indriya is “seen in the four jhānas”. Three other discourses in the same collection (SN 48.9, SN 48.11, and SN 48.50) define this indriya as when a “noble disciple gains concentration, gains one-pointedness of mind (cittassa ekaggataṃ), having made release the object.” SN 48.10 (at SN V, 198) combines the latter definition with the standard detailed description of the four jhānas.
Although it can’t be stated conclusively that the indriya of samādhi is equated with the four jhānas, it seems to have a stronger connection with them in the discourses than sammā samādhi does.
Regarding the difference between samādhi and jhāna, it seems to me that samādhi is a quality of mind from which the jhānas can be developed (and from which many other things can be developed too, as evidenced by the many different types of samādhi described in the discourses). One main difference between descriptions of samādhi and descriptions of jhāna is that jhāna descriptions emphasize seclusion, perhaps signifying a deeper, more cocooned mind state.