What does 一層 mean?
一層 is a Japanese noun meaning “much more, still more” in English. It can also be translated as “one layer, lowest floor (of a building), rather” depending on context. It is written as 一層 in kanji, いっそう in hiragana, and issou in romaji. This word is part of JLPT N3 vocabulary.
Example sentence
今まで以上にいっそう勉強に励みなさい。
You should study even more than before.