A word for a “series”, most notably used in names of the series (columns) of the tengwar chart: tincotéma, parmatéma, and so forth (LotR/1118). In The Etymologies of the 1930s, ᴹQ. téma was given larger set of glosses: “row, series, line” (Ety/TEÑ). I believe téma means “line” only in the sense of a series of discrete items in a row such as a line of people, as opposed to [ᴹQ.] tea for a continuous straight line.

Possible Etymology: In The Etymologies of the 1930s, ᴹQ. téma was derived from the root {ᴹ√TEƷ >>} ᴹ√TEÑ “line, direction” (Ety/TEÑ), probably from primitive {*teʒmā >>} *teñ-mā where the ancient ñ/ʒ vanished with compensatory lengthening. This worked perfectly fine when the root was ᴹ√TEƷ, but this transition no longer worked properly after the root became ᴹ√TEÑ. For example, in the Outline of Phonetic Development (OP1) from the 1940s, Tolkien said that the usual development was ñm > ñw > ñgw, though he did say that ḗma was sometimes the result analogical reformations:

But note before suffixed n, m the nasality of [ñ] was originally preserved, so that eñ-ma > eñwa > eñgwa; ḗma was here an analogical formation proceeding from medial forms with lost [ñ] via [ʒ] (PE19/47).

These issues seemed to have pushed Tolkien to look for alternate etymologies of this word. In the second version of Tengwesta Qenderinwa (TQ2) from around 1950, he again derived tēma from teʒmā:

Medially ñ, ʒ only coalesce between vowels, and before r, l {or before m, n} when both vanish with compensatory lengthening of preceding vowel. Before nasals n, m: ʒ vanished with compensatory lengthening very early, hence teʒmā > tēma, but ñ remained and fell in with products of g (k): teñma, tegma, tekma all > teñma > teñgwa (PE18/104).

The deletion {or before m, n} in the above note indicates Tolkien was vacillating on the development of ñm. Similar vacillations appeared in the Outline of Phonology (OP2) from the early 1950s. Towards the beginning of this document Tolkien wrote:

ñm, ñn: here (though spelling with ŋ was retained to indicate nasality) ñ ceased to be consonantal and the preceding vowel became nasalized, and lengthened if short: as teŋ-mā > tę̄ma (PE19/82).

But later in the same document Tolkien wrote:

In these cases the historical results were the same as for stops + mn. mn, mm, nn remained unchanged. nm > nw. ñm > ñw > ññw > ñgw [my emphasis]. ñn > n (with lengthening of a preceding short vowel) after ī̆, ū̆; but nn after e, a, o (PE19/97 note #136).

Immediately after this Tolkien gave yet another etymology of téma “series”, this time from the root √TEG :

Owing to the disappearance of medial ñ the historical developments retaining a stem-nasal were specially liable to later alteration. Thus tēma, series, fr[om] TEG- “line”: tegma “direct[ion], process” > teñma > tę̄ma. Thus eñma > eñgwa might be re-formed to éma after eñ- > é (PE19/97 and note #138).

Thus it seems Tolkien went back to the scenario where téma is the result of some analogical reformation. However, in lengthy green-ink revisions of OP2 from around 1970, Tolkien changed his mind again:

ñm, ñn originally remained but iŋ, uŋ early became nasalized ī̜, ų̄ (the nasality being still retained in Noldorin), later eŋ, aŋ, oŋ became en, an, on by forward assimilation before n, but eŋ, aŋ, oŋ + m became long ę̄, ą̄, ǭ; the spellings ŋm, ŋn were usually retained in PQ (PE19/96-97).

After this revision, Tolkien deleted the statement whereby “eñma > eñgwa might be re-formed to éma after eñ- > é”, since in this new scenario tegma > teñma > tę̄ma was the normal development and no reformation was required.

To summarize:

• In The Etymologies of the 1930s, téma was based on ᴹ√TEÑ {<< ᴹ√TEƷ}, but its phonetic developments aligned better with primitive *teʒmā (Ety/TEÑ).
• In the second version of Tengwesta Qenderinwa (TQ2) from around 1950, Tolkien derived téma from ✶teʒmā (PE18/104).
• In the Outline of Phonology (OP2) from the early 1950s, Tolkien derived téma from ✶tegma but said the long é was a reformation since normally gm > ñm > ñgw (PE19/97 note #136 and #138).
• In green-ink revisions to OP2 from the early 1950s, Tolkien revised the sound changes for ñm so that tegma > teñma > tę̄ma was the normal phonetic development (PE19/96-97).

Note that there were similar vacillations for the etymology of tengwa “letter”; see that entry for discussion.

Neo-Quenya: For purposes of Neo-Quenya, I assume that téma is derived from primitive tegmā based on √TEG “line”. However, I retain the phonetic developments gm > ñm > ñw > ñgw, and therefore stick to the scenario where téma “series” is some kind of variant development or reformation.