沛 rarely stands alone in modern Chinese; you almost always meet it inside the compound
充沛 (chōngpèi, 'abundant/full of') —
精力充沛 (energetic),
雨水充沛 (plentiful rainfall). It's also a place name:
沛县 (Pèi Xiàn) in Jiangsu was the birthplace of Han dynasty founder Liu Bang, hence his nickname
沛公 (Lord of Pei).