Simple past tense and past participle of slick. (verb)
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Use "slicked" in a sentence
"He reappeared with his hair well "slicked," his tip-tilted nose as pink as his shiny cheeks, and a smile that extended to the furthest confines of his face."
"Imagine a tall young fellow, with a thin face, lantern jaws, and long hair 'slicked' down on either side."
"He had 'slicked' his hair down with the fresh water; he had adjusted his neck-handkerchief, and borrowed an odd candle-end to polish his clogs with and there he sat, enforcing some opinion on her father, with a strong Darkshire accent, it is true, but with a lowered voice, and a good, earnest composure on his face."