√AMA root. “addition, increase, plus”
In a 1965 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.
References ✧ PE17/91, 146