From chala'; properly, disease; hence, rust -- scum.
see HEBREW chala'
H2457. chelah
I. [חֶלְאָה] noun feminine rust (perhaps as filth see above) — חֶלְאָתָהּ Ezekiel 24:6, 12 + 24:11; 24:12 (strike out Co internal grounds) + 24:6 חֶלְאָתָהֿ (compare Ges§ 91, 1; R. 2) rust on metal pot, symbol of impurity of Jerusalem.