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.
irt
noun. beak (of small birds)
irtha-
verb. to peck
A verb appearing as G. {irta- >>} irtha- “peck” in the Gnomish Lexicon of the 1910s (GL/52), probably based on the early root ᴱ√ᴵRTYᴵR “peck, prick” from the contemporaneous Qenya Lexicon (QL/43).
Neo-Sindarin: I would retain this verb as ᴺS. irtha- “to peck” based on the Neo-Root ᴺ√IRIT “peck, prick”.
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.
A noun appearing as G. irt⁽⁾ “beak (of small birds)” in the Gnomish Lexicon of the 1910s (GL/52), clearly based on the early root ᴱ√ᴵRTYᴵR “peck, prick” (QL/43). There was no irt⁽¹⁾.
Neo-Sindarin: For purposes of Neo-Sindarin, I would adapt this word as ᴺS. irth “beak” based on the Neo-Root ᴺ√IRIT; compare S. amarth < ✶(a)mbarta.