ᴹ√SUB root. “sink (esp. in water)”
The root ᴹ√SUB “sink, esp. in water” appeared in a rejected page of verbal roots from the Quenya Verbal System of the 1940s where it had a derived past tense form ᴹQ. sumbe “*sank” as well as a distinct verb form ᴹQ. sumba- “to submerge” (PE22/127). It might be a later iteration of the unglossed root ᴱ√SUQU in the Qenya Lexicon of the 1910s, with derivatives like ᴱQ. sunqa “going down, descending; abysmal, deep, profound” and ᴱQ. suq- “fall, fail, go down, die down” (QL/87).
Neo-Eldarin: I think it is worth retaining ᴺ√SUB “sink” as a Neo-Root.
Reference ✧ PE22/127 ✧ “sink (esp. in water)”
ᴱ√SUQU root. “*descend”
Reference ✧ QL/87