- 大海捞针 dàhǎilāozhēn needle in a haystack(idiom) like fishing a needle from the sea; a difficult or impossible task where the chances of success are extremely small
- 汪洋大海 wāngyángdàhǎi vast oceana vast and boundless ocean
- 石沉大海 shíchéndàhǎi to elicit no responseLiterally "a stone sinking into the great sea"; used to describe someone or something that has disappeared without a trace or a message that has received no reply.
- 胖大海 pàngdàhǎi malva nutthe seed of the boat-fruited sterculia tree, used in Chinese medicine and known for expanding into a sponge-like mass when soaked in water
- 石投大海 shítóudàhǎi to vanish foreverto disappear completely like a stone dropped into the ocean; to elicit no response and never be heard from again
- 大海里捞针 dàhǎilǐlāozhēn to look for a needle in a haystackto fish for a needle in the ocean; a metaphor for something extremely difficult to achieve or nearly impossible to find; often used as the first half of a two-part allegorical greeting (xiehouyu) where the second half is [[难上难|難上難|nan2 shang4 nan2]]
- 大海沟 dàhǎigōu marine trenchdeep-sea trench; marine trench
- 膨大海 péngdàhǎi malva nutThe seed of the malva nut tree, used in Chinese medicine to treat sore throats; same as [[胖大海|胖大海|pang4 da4 hai3]]
