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!

Gnomish

thlib-

verb. to sup, lap up, suck

The verb G. thlib- {“sup, sip” >>} “sup, lap up, suck” appeared in the Gnomish Lexicon of the 1910s which Tolkien said was the equivalent of ᴱQ. salpi (GL/73), thus clearly based on the early root ᴱ√SḶPḶ (QL/84).

Neo-Sindarin: The early root ᴱ√SḶPḶ became ᴹ√SALAP “lick up” in The Etymologies of the 1930s, so I would adapt this verb as ᴺS. lhab- from ✱s’lap-, but I would use it mainly with the sense “sup, sip” while for “lap up, suck” I’d use ᴺS. lavra-. I’d also assume a noun form ᴺS. lhab “a sip”, to justify the abnormal vocalization of the verb.