A noun in The Etymologies from around 1937, glossed “pollen, yellow powder” and derived from the root ᴹ√SMAL “yellow” (Ety/SMAL).

Conceptual Development: In Tolkien’s earlier writings, ᴱQ. malo was “rust”, first appearing in the Early Qenya Grammar and Early Qenya word-lists of the 1920s (PE14/42, 44, 71, 74; PE15/77; PE16/111) and later as ᴹQ. malo “rust” in the Declension of Nouns of the early 1930s where it had a stem form of malu- (PE21/12). Most likely these earlier forms were based on the early root ᴱ√MALA² “yellow” from the Qenya Lexicon of the 1910s (QL/63), though in QL itself the word ᴱQ. malo was “moth” from the distinct root ᴱ√MALA¹ “crush” (QL/63).

Neo-Quenya: For purposes of Neo-Quenya, I think the “pollen” and “rust” meanings for malo (malu-) can co-exist, with both originally considered a form of “yellow powder”.