A number of translators have asked me abouyt this word recently. It seems to come from "mel" ("mill"-- "meltsuker" is another word for "granulated sugar", and/or related to the Slavic измельчать (izmel'chat') to grind/crush). I've encountered the word myself more often in Southern dialects of Yiddish, such as in the writing by Bessarabian authors Yekhiel Shraybman (see the the example from "A Hozime" above) and Moyshe Altman, and in the speech of native Yiddish speakers from Moldova and the Podolia region of Ukraine. In the latter category, the word seems to used colloquial to mean "sugar" whether granulated or not. In Southern dialects, the word would be pronounced "meylets"