お元気で
おげんきで · ogenkide · JLPT N2 · noun
care
元気 = 元 origin + 気 energy: go on, keeping your energy whole
お adds politeness and で means in that state, so お元気で is (stay) in good health. It's a farewell for longer partings, when you won't see someone for a while, unlike a casual じゃあね.
元 — 二 (two) + 兒 variant 儿 (legs/person)
元 originally depicted a person with the head emphasized on top, meaning 'head' or 'origin'. From this came the extended senses of 'first', 'beginning', and 'primary'. It was later borrowed as the name of the Yuan dynasty and the modern Chinese currency unit.