Early Quenya
millo
noun. oil
ilma
noun. oil
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 ᴱQ. millo “oil” appeared in Early Noldorin Word-lists of the 1920s as a cognate of ᴱN. bliw, both derived from primitive ᴱ✶mḷgo (PE13/139). In the Qenya Lexicon of the 1910s the word for “oil” was ᴱQ. ilma derived from the early root ᴱ√ILI “shine oily” (QL/42).
Neo-Quenya: For purposes of Neo-Quenya I’d retain ᴺQ. millo for “oil” from a Neo-Root ᴺ√MILIG, where lg became ll (PE19/93). However, I would assume a stem form of millu- and a primitive form ✱mil’gu to better explain the final w in ᴺS. blîw “oil”.