A negation of cárima “feasible, possible”, first appearing as ᴹQ. alkárima “impossible to make” in the Quenya Verbal System (QVS) of the 1940s (PE22/111), then as Q. la-kárima “not feasible, impossible” in Late Notes on Verb Structure (LVS) from around 1969 (PE22/153). The 1969 variant appeared in a paragraph which started “As a prefix the reduced form la (short a) appears. This is used with verbal derivatives, nouns or adjectives ...”, but Tolkien rejected this paragraph. The new version of the paragraph read “With nouns and adjs. (not regularly attached to verbal stems, such as -ima, -ite) the form was al before vowels and usually (in all later and free formations) before initial consonants that in Q. were permitted after l”. Thus it seems likely alcárima was restored, although it did not appear in the revised paragraph.

Neo-Quenya: For purposes of Neo-Quenya, I would use the 1940s form ᴺQ. alcárima with the 1969 meaning “not feasible, impossible”.