modest
Not bragging about yourself, or being small and simple.
Modest means not boasting or drawing attention to yourself, even when you have good reasons to feel proud. When you win a spelling bee and someone congratulates you, a modest response might be “Thanks, I got lucky with the words” rather than “I'm the best speller in the whole school.”
The word also describes something small or limited in size or amount. A family might live in a modest house that's comfortable but not fancy. A student might make modest progress in piano, getting a little better each week without any dramatic breakthroughs.
Being modest doesn't mean hiding your abilities or pretending you're not good at things. It means being honest about your strengths without making everything about you. When a basketball player scores the winning shot but tells reporters, “My teammates set me up perfectly,” that's modesty. She's not denying what she did, she's just not grabbing all the credit.
The opposite of modest is boastful or arrogant. Someone who constantly reminds everyone how smart or talented they are isn't being modest. True modesty can make people respect you more, because it shows you can be good at something without needing constant attention for it.