ᴺS. [G.] lui n. “blueness; livor, livid mark, *bruise” (Category: to Wound; Wound; Wounded)
A noun appearing as G. lui “blueness, livor, livid mark” in the Gnomish Lexicon of the 1910s (GL/55), hence = “*bruise”.
Neo-Sindarin: Since √LUY remains the root for “blue” in Tolkien’s later writing (VT48/23), I’d adapt this word as ᴺS. lui “blueness; livor, livid mark, *bruise”. Likely “blueness” was the original sense, extended to include blue-coloured bruises on the body.
Reference ✧ GL/55 ✧ “blueness, livor, livid mark”