What does 精通 mean?
精通 is a Japanese noun meaning “being well versed (in); being well acquainted (with); being familiar (with); having a thorough knowledge (of)” in English. It can also be translated as “(a boy's) first ejaculation” depending on context. It is written as 精通 in kanji, せいつう in hiragana, and seitsuu in romaji. This word is part of JLPT N4 vocabulary.
Example sentence
彼は英語に精通している。
He is quite at home in English.