滄海〔沧-〕 cong¹ hoi² {cāng hǎi}

the vast ocean

滄海橫流〔沧-横-〕 cong¹ hoi² waang⁴ lau⁴ {cāng hǎi héng liú}

to describe political / chaos in society; stormy; turbulence in the sea

滄海一粟〔沧---〕 cong¹ hoi² jat¹ suk¹ {cāng hǎi yī sù}

a drop in the ocean (idiom)

滄海桑田〔沧---〕 cong¹ hoi² song¹ tin⁴ {cāng hǎi sāng tián}

1. lit. the blue sea turned into mulberry fields (idiom)
2. fig. the transformations of the world

滄海遺珠〔沧-遗-〕 cong¹ hoi² wai⁴ zyu¹ {cāng hǎi yí zhū}

undiscovered talent (idiom)