Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
mellum, i, n., a dog’s collar, Varr. R. R. 2, 9, 15 Schneid. N. cr. (al. melium and maelium).
Also, millus, i: millus collare canum venaticorum, factum ex corio confixumque clavis ferreis eminentibus adversus impetum luporum, Paul. ex Fest. p. 151 Müll.
Also written melium, mil-lus, q. v.