大王 (dàwáng) is a noun meaning "king" or "great king," used as a respectful or elevated title for a ruler. It is more formal and deferential than 王 alone. It appears frequently in classical stories and historical narratives.
大王,敌军已经到了城门外了。
dàwáng, díjūn yǐjīng dàole chéngmén wài le.
Your Majesty, the enemy troops have already reached the city gate!
大王下令让所有士兵准备迎战。
dàwáng xiàlìng ràng suǒyǒu shìbīng zhǔnbèi yíngzhàn.
The king ordered all soldiers to prepare for battle.
故事里的大王非常喜欢赛马。
gùshì lǐ de dàwáng fēicháng xǐhuān sàimǎ.
The king in the story loved horse racing very much.