马上(mǎ shàng) - immediately, right away, at once in Mandarin

马上 (mǎshàng) 'immediately' literally means 'on (a) horse' (马 horse + 上 on top), the idea being that something done while still mounted, ready to ride off, happens at once. 马 is a pictograph of a horse and 上 is a simple indicative for 'up, on'.

Origin

compound

Root

马 (horse) + 上 (on top, up)