A root that was a later entry in The Etymologies of the 1930s glossed “call to, summon, name by name” and having rejected variants ᴹ√KHAL², ᴹ√KYAM and ᴹ√KHEM. Tolkien’s introduction of this root seems to have caused him to restore ᴹ√KHAD over ᴹ√KHAM “sit”; see the entry on √KHAD for further discussion. Meanwhile, ᴹ√KHAM² was probably introduced to explain ᴹQ. nahamna “summoned” in the version of the Lament of Atalante from the 1930s (LR/47). The phrase where it appeared underwent quite a few changes thereafter, ultimately becoming ar Sauron túle nukumna Númenórenna “and Sauron came humbled [to Númenor]” by the 1940s, so the future status of ᴹ√KHAM² “summon” is unclear.
It is a useful root for purposes of Neo-Eldarin, however, and I think it is worth retaining.