Something that is part metal and part something else, like a metal and a non-metal mixed together.
Semimetallic things are often used in science and technology.
Examples:
The semimetallic substance is used in making computer chips.
The semimetallic rock is very shiny.
The semimetallic material is very strong.
I found a semimetallic thing in the ground!
The spaceship is made of semimetallic stuff.
The robot's body is semimetallic and shiny.