An adverb meaning 'even more' or 'all the more'; used to indicate a stronger degree or intensity than before.
最近の気温は去年より一層高くなっている。
Recent temperatures are even higher than last year.
彼の説明を聞いて、問題が一層はっきりした。
After listening to his explanation, the problem became all the more clear.
試合に負けてから、彼は練習に一層励むようになった。
After losing the match, he began to train even harder.
A noun meaning 'one layer' — a single stratum or tier in a layered structure.
このケーキは一層目にイチゴが挟んである。
This cake has strawberries between the first layer.
断面を見ると、塗料が三層に分かれていて、一層だけ剥がれていた。
Looking at the cross-section, the paint is split into three layers and only one layer had peeled off.
A noun meaning 'the lowest floor' of a building (in some contexts used like 'first floor').
工場の一層は倉庫として使われている。
The lowest floor of the factory is used as a warehouse.
そのビルの一層に受付があります。
The reception is on the ground (lowest) floor of that building.
An archaic adverb meaning something like 'rather' or 'preferably' (similar to いっそ). This usage is now largely obsolete.
古い文献では『一層〜すべし』のような表現が見られる。
In old documents you can find expressions like '一層〜すべし' (meaning 'it would be better to...').