同心 literally means 'same heart' and is used to describe people or groups that are united in purpose, working together with a shared goal. It often appears in set phrases like 同心协力 (tóng xīn xié lì, 'make concerted efforts'). In geometry, it means 'concentric', as in 同心圆 (tóng xīn yuán, 'concentric circles'). As a stative verb, it can be used predicatively ('他们很同心') or attributively with 的.