Gnomish
rig
noun. a snarl, a sneer
rig-
verb. to twist, contort
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!
A verb appearing as G. rig- “twist, contort” in the Gnomish Lexicon of the 1910s (GL/65). It was clearly based on the early root ᴱ√RIKI from the contemporaneous Qenya Lexicon of similar meaning; compare ᴱQ. riqi- “wrench, twist” (QL/80). The Gnomish verb had a longer variant rictha- “contort, twist” which also had an extended meaning “confuse, disarrange, upset”.
Neo-Sindarin: The root √RIK “twist” survived in Tolkien’s later writings, so I would retain ᴺS. rig- “to twist, contort” for purposes of Neo-Sindarin, but I would also give it the extended meaning “✱to confuse, disarrange, upset” from its longer Gnomish variant.