Gnomish
raibrog
noun. zebra
ribrog
noun. zebra
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 word for “zebra” in the Gnomish Lexicon of the 1910s was raibrog or ribrog with a feminine variant raibros, a combination of G. raib “striped” and G. brog “horse” (GL/64).
Neo-Sindarin: I’d adapt this word as ᴺS. raebroch for purposes of Neo-Sindarin, using the later word S. roch for “horse”.