소심하다 means "to be cautious," or "to be self-conscious." 소심 literally means a small heart. The 소심한 person tends to be quiet/reserved and think many times before action. Examples) 그는 돈에 소심해요: He is cautious with money (He is careful with money). 소심해서 수업시간에 질문을 못해요: I am self-conscious, so cannot ask questions during class.