The root ᴹ√SAM “unite, join” was a later addition to The Etymologies of the 1930s with the derivative ᴹQ. samnar “diphthongs” (Ety/SAM). There is also evidence for it in the word ᴹQ. sampane “combination” as in ᴹQ. Lámasampane “Combination of Sounds”, a term used in the first version of the Tengwesta Qenderinwa (TQ1) from the 1930s (PE18/40), and again in the second version (TQ2) from around 1950 (PE18/90). In an isolated note from the late 1930s, Tolkien gave ᴹ√kam “bind, join” as a replacement for √sam along with a new word ᴹQ. okamna “diphthong” (VT44/13), but given the reappearance of Q. sampanë in TQ2 this may have been a transient idea, and in any case Tolkien used the word Q. ohlon for “diphthong” in the 1950s and 60s (VT39/9; VT48/29).

In notes grouped with Definitive Linguistic Notes (DLN) from 1959, Tolkien gave √SAM as the basis for Elvish verbs for “to have”, with Q. samin and S. sevin “*I have” (PE17/173). Whether this was connected to 1930s ᴹ√SAM “unite, join” is unclear. In notes associated with the 1959-60 essay Ósanwe-kenta, Tolkien gave the root √SAM with the gloss “mind, think, reflect, be aware” (VT41/5), but in later writings he used √SAN for “think, use mind” instead (PE22/158); see that entry for discussion.

Neo-Eldarin: For purposes of Neo-Eldarin, I’d use √SAM = “have”.