A lintel is a type of beam (a horizontal structural element) that spans openings such as portals, doors, windows and fireplaces.
Mnemonic
[m-] Mario is [2] inside the [-(e)i] beach house by the bay installing a 楣 lintel above one of the beach house entryways. The 楣 lintel is a small dead 木 tree that is driftwood and sandy that washed up on the beach earlier that day. Mario uses some flames to melt it into place above the entrance, and then decorates it with sea shells. He accidentally burns off one of his 眉 eyebrows in the process. Done, Mario looks at the new 楣 lintel and thinks to himself that a 楣 lintel is like an 眉 eyebrow, but for entryways and doors. It's true.