Simple past tense and past participle of scum.(verb)
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Use "scummed" in a sentence
"Clutching the woodwork of the galley for support, — and I confess the grease with which it was scummed put my teeth on edge, — I reached across a hot cooking-range to the offending utensil, unhooked it, and wedged it securely into the coal-box."
"We found him, when we went to search for him, face downward in a little green-scummed pool, which lay at the foot of the garden."
"From the end of it a small wand planted here and there showed where the path zig-zagged from tuft to tuft of rushes among those green-scummed pits and foul quagmires which barred the way to the stranger."