Gnomish
thlib-
verb. to sup, lap up, suck
-thlib
suffix. -ly or -like
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
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.