mack
n. countablen. a very large truck used for carrying heavy loads over long distances. In the US, people often use this name because it is a famous brand of big trucks.
n. a heavy-duty truck or tractor-trailer, typically of the brand manufactured by Mack Trucks. Often used metonymically in North American English to refer to any exceptionally large or powerful vehicle.
A huge Mack truck drove past us on the highway.
The construction site was filled with heavy machinery, including a Mack truck hauling tons of gravel.
The impact of the news hit him like a Mack truck, leaving him momentarily stunned and unable to process the sudden shift in his professional circumstances.
(In sense one) From either the male name Mack or mack, itself from mackerel, which comes from Old French maquerel, from Dutch makelaar. Compare French mec.
Often used in the idiom 'hit like a Mack truck' to describe a powerful physical or emotional impact.