Meaning
A rectangular flap mounted near the wheel of a motor vehicle (especially a truck) to prevent mud or rocks from being thrown up (by the wheel), either onto the body panels or into the path of vehicles following behind.
Etymology
Origin: Unknown
From mud + flap.
NYT Puzzle Appearances
No published puzzle dates on file for this word yet. It is part of the official NYT Spelling Bee word list for 2019, 2020.