sturdy
Strong and solid, able to last without breaking easily.
Sturdy means strong and solidly built, able to withstand pressure, weight, or rough treatment without breaking or falling apart. A sturdy wooden table won't wobble when you lean on it. A sturdy pair of boots will last through years of hiking, puddle-jumping, and hard wear.
The word describes both physical objects and people. A sturdy bridge can hold heavy trucks safely. A sturdy rope won't snap when you climb it in gym class. When describing a person, sturdy suggests someone with a strong, solid build who looks capable of hard physical work or outdoor activity.
You can also use sturdy to describe things that aren't physical. A sturdy argument is one that holds up well when challenged, built on solid reasoning and good evidence. A sturdy friendship weathers disagreements and difficulties without falling apart.
The opposite of sturdy is flimsy or fragile. A flimsy chair might collapse under your weight, while a sturdy one will support you reliably. When you're building something, whether it's a treehouse, a robot for a school project, or an explanation of why your answer is correct, you want it to be sturdy enough to last and do its job well.