muck meaning, definition, what is muck: mud, dirt, or a sticky natural substance such as animal waste. Learn more. Muck is mud, wet manure, or a black dirt made up of rotting plant material. An example of muck is the sticky thick ground in a cow field after the rain. An example. muck in meaning, definition, what is muck in: to share the work that needs to be done. Learn more. Is it wrong to use 'decimate' to mean 'destroy'? An example of muck is the thick mud that forms underneath a pile of leaves. Trends of 'muck in'. Behave in a silly or aimless way. Its fridaycourse we're muckin Winston's tonight. What does sowback mean? Language expert Ian Brookes looks at the word 'election' and its origins.