Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!

Qenya 

suv-

verb. to sink (esp. in water)

A verb appearing on a rejected page of verbal roots in the Quenya Verbal System (QVS) from 1948, given only in its past form ᴹQ. sumbe based on the root ᴹ√SUB “sink, esp. in water” (PE22/127). Presumably its stem form would be ✱suv- “to sink”.

Conceptual Development: The Qenya Lexicon of the 1910s had ᴱQ. suq- “fall, fail, go down, die down” under the early root ᴱ√SUQU (QL/87). Related words had to with the setting sun and stars rather than sinking in water.

Neo-Quenya: I retain ᴺQ. suv- “to sink (especially in water)” for purposes of Neo-Quenya, as similar verbs mostly have to do with descending objects like the setting sun rather than sinking in liquid.