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 

sumba-

verb. to submerge

A verb given as ᴹQ. sumba “to submerge” in the margins of a rejected page of verbal roots in the Quenya Verbal System (QVS) from 1948, derived from the root ᴹ√SUB “sink, esp. in water” (PE22/127).

Neo-Quenya: I retain ᴺQ. sumba- “to submerge” for purposes of Neo-Quenya, since the closest other verb (Q. undulav- “down-lick = drown, swallow, submerge”) has other connotations.