an oil slick

the slick is a serious threat to marine life

an application or amount of a glossy or oily substance

a slick of lip gloss

a racing-car or bicycle tyre without a tread, for use in dry weather conditions

Hunt's victory resulted from the finest sort of judgement about when to change his wet tyres to slicks

a glossy magazine

writing for any of the so-called slicks was considered selling out

a person who is smooth and persuasive but untrustworthy

make (one's hair) flat, smooth, and glossy by applying water, oil, or gel to it

his damp hair was slicked back

his slicked-down hair