海|うみumi[1]atamadaka (head-high)

1. nounsea; ocean; waters
   何なんとしても海うみをひと目めみたいものだ。↗

   I ache for a sight of the sea.

• Synonym海洋かいようWrittenSino-Japanese word for academic and formal contexts, as in 「海洋学」「海洋汚染」; 「海」 is the everyday word.
• Synonym海原うなばらWrittenA vast, boundless expanse of open sea, as in 「青い海原」; carries a literary flavor.
• Synonym大洋たいようWrittenA geographic term for the great oceans, e.g. the Pacific, as in 「五大洋」.
• Synonym大海たいかいNeutralA vast sea; often seen in the proverb 「井の中の蛙大海を知らず」, with a metaphorical flavor.
• SynonymオーシャンNeutralA loanword seen mostly in names, as in 「オーシャンビュー」.
• Synonym大海原おおうなばらWrittenAn emphatic 「海原」 for a sea stretching beyond sight; lyrical in tone.
• Antonym陸りくNeutralRead 「ろく」, it is colloquial and appears in 「ろくな～ない」 ('no decent…'); it is not the opposite of 「海」. Only written 「陸」, meaning land, contrasts with it.
• AntonymやまNeutralThe opposite of 「海」, often paired with it as 「山と海」; refers to mountains.

Use 「海」 by default. Pick 「海洋」 in academic or formal contexts, 「大洋」 for the geographic oceans, and 「海原」 or emphatic 「大海原」 for a literary, sweeping sea. 「大海」 and 「オーシャン」 appear in set phrases and names; 「陸」 and 「山」 are opposites, not substitutes.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. うみ。海洋かいよう。
2. 硯すずりの表ひょうにある窪くぼみで、墨液ぼくえきを溜ためる部分ぶぶん。