For most of Tolkien’s life, the Primitive Elvish root for “mother” was √AM. This began with the Qenya Lexicon of the 1910s, where Tolkien gave the root as ᴱ√AMA (QL/30). In The Etymologies of the 1930s it was ᴹ√AM with derivatives ᴹQ. amil and (archaic) N. emil “mother” (Ety/AM¹). In Quenya prayers of the 1950s, the word for mother was Q. Amille. In the last few years of his life, however, Tolkien toyed with the notion of changing this root to √EM. In notes associated with Eldarinwe Leperi are Notessi written in the late 1960s, Tolkien first gave the root as am, but then wrote em next to it with a question mark, along with several new em-derivatives (VT48/19 note #16). The Q. affectionate word emme for “mommy” appeared in the main article, indicating Tolkien did, in fact, adopt this new root, at least for some period of time.
Neo-Eldarin: For purposes of Neo-Quenya writing, I personally prefer to ignore this late change to the root for “mother” and stick with the √AM-forms Tolkien used for most of his life. However, the √AM-forms were less stable in the Sindarin branch of the languages, so I’d use √EM-forms like S. emel and emig, and would assume √AM and √EM were variants of the root, as they were on VT48/19 (see above).
In a 1967 note on comparison, Tolkien said:
> But there existed a “base” that was intrinsically “comparative”, √AMA. This signified addition, increase, plus (PE17/91).
Very likely this was a variant or extended meaning for the root √AM “up”, perhaps with the basic sense “more”, as in the derived words Q. ambë (adverb) and amba (adjective) of that meaning (PE17/91). Tolkien seems to have introduced this additional meaning to the root √AM as part of a new etymology for the Q. intensive prefix an-. With this new derivation, the intensive prefix became am(a)-. See the entry on the Q. comparative for a discussion of the conceptual development of this intensive/comparative prefix.
Neo-Eldarin: For purposes of Neo-Eldarin, I think it is preferable to retain the older derivation of the intensive prefix an-, especially for compatibility with possible Sindarin intensives like S. anfaug “gasping” and S. einior “elder” (though the latter could be derived from ✱amyāra). Intensive an- also helps avoid confusion with the prefix am- “up”. But I would retain some of the very useful derivatives of the root √AMA, notably Q. ambe/amba “more” given above, perhaps with new etymologies from ✱an-bē and ✱an-bā.