committed
Very dedicated and willing to keep working at something.
Committed means dedicated to something with serious intention and follow-through. When you're committed to learning piano, you practice regularly, even when it's hard or you'd rather be doing something else. When a friend commits to helping you with a project, they show up and do their part.
The word carries more weight than interested or involved. Someone might be interested in joining the soccer team, but a committed player attends every practice, works on skills at home, and doesn't quit when the team loses a few games. A committed student completes every assignment thoroughly and on time.
People can be committed to goals, relationships, causes, or principles. A scientist might be committed to finding a cure for a disease and work for years despite setbacks.