sea of words; vast vocabulary
Idiomatic expression likening a large collection or expanse of words to a sea. Often used metaphorically for dictionaries, literature, or someone's extensive vocabulary.
This dictionary is truly a sea of words.
Inside his head, a sea of words stretches out.
Compound of 言葉 (kotoba, 'word') + の (no, possessive particle) + 海 (umi, 'sea'). The metaphorical use of 'sea' to describe a vast expanse is common in Japanese.