Especially; particularly; notably (used mainly in written/formal contexts).
この実験は殊に第三段階が重要だ。
This experiment is especially important in the third stage.
体調管理が大切だ。殊に冬場は風邪に注意すること。
Health management is important. In particular, be careful of colds during winter.
彼の作品はどれも良いが、殊に初期の作品が評価されている。
All of his works are good, but his early works are particularly appreciated.
Additionally; moreover (archaic usage, rarely used in modern Japanese).
古文では『殊に』が『加えて』の意味で用いられる例がある。
In classical texts, '殊に' is sometimes used with the meaning 'additionally'.