A verb in the Gnomish Lexicon of the 1910s appearing as G. {sûtha- >> sû- “wash clean” and sôtha- “bathe (tr. & intr.)” >>} sô- “wash clean, bathe (tr. & intr.)”, all based on the early root ᴱ√soƀ (GL/68). Likely the long ô is the result of the sound change whereby ou became ō as was usual in Gnomish of the 1910s.
Neo-Sindarin: In later Sindarin ancient ou became ū which produces problematic verb forms, so I would instead adapt this verb as ᴺS. sov- “to wash clean, bathe” as a cognate to ᴺQ. sov- “✱to bathe”. See also ᴺS. whal- “to wash”.
A verb appearing as G. sûtha- “blow (of wind)” in the Gnomish Lexicon of the 1910s (GL/68), related to G. sû “noise of wind” and thus probably based on the early root ᴱ√SUH(Y)U (QL/86) as suggested by Christopher Tolkien, though he miswrote this verb as súltha (LT1A/Súlimo).
Neo-Sindarin: For purposes of Neo-Sindarin I would update this verb to ᴺS. súda- “to blow (of wind)”, since √SŪ “move with audible sound (of air)” survived in Tolkien’s later writings, but -tha was no longer a common verbal suffix in Sindarin of the 1950s and 60s.