1. clag - Noun
2. clag - Verb
A glue or paste made from starch.
Low cloud, fog or smog.
(railway slang) Unburned carbon (smoke) from a steam or diesel locomotive, or multiple unit.
(motor racing slang) 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).
He ran wide in the corner, hit the clag and spun off.
(obsolete) To encumber
To stick, like boots in mud
Source: en.wiktionary.org