To make something stronger or more solid.
Sturdied things are less likely to break or fall over.
Examples:
He sturdied the table so it wouldn't wobble.
The builder sturdied the house with extra beams.
She sturdied the shelf with more nails.
I sturdied my sandcastle so it wouldn't fall down.
The superhero sturdied the bridge so it wouldn't collapse.
The tree sturdied itself by growing more roots.