正常
zhèngcháng · HSK 2
regular
正 = upright/correct + 常 = constant/usual = normal
正 means upright or correct; 常 means constant or ordinary (think 常常 'often'). Together 正常 is what is correct-and-usual, i.e. normal or regular. Opposite of 反常 (abnormal).
正 — one 一 + stop 止
Originally an ideograph showing a foot (止) advancing toward a target line (一), meaning 'to march straight toward' a city or goal. From this came the senses 'upright,' 'correct,' and 'proper.' The military sense survives in 征 (to campaign), which took over the original 'march' meaning.
常 — 巾 (cloth) + 尚 (phonetic, 'esteem')
Originally written 裳, 常 was a phono-semantic compound: 巾 ('cloth') gave the meaning and 尚 supplied the sound, referring to a long lower garment or skirt. Over time the meaning shifted from 'everyday garment' to 'ordinary, regular, constant', while 裳 took over the original clothing sense.