Low cloud, fog or smog.
Unburned carbon (smoke) from a steam or diesel locomotive, or multiple unit.
Bits of rubber which are shed from tires during a race and collect off the racing line, especially on the outside of corners (cf. marbles).
A glue or paste made from starch.
To stick, like boots in mud
The state of being cloudy (e.g. weather).
The property of being murky (e.g. liquid, style).
The property of being obscure (e.g. information).