A door jamb is literally the door's "leg" — from the same root as the viola da gamba (leg viol) and the chess term gambit (tripping the leg).
The vertical side post or surface of a doorway, window, or fireplace opening.
From Old French jambe (leg, pier, side post of a door), from Late Latin gamba (leg, hoof), from Greek kampē (κάμπη, a bending, a joint). The architectural sense derives from the image of the doorway's side posts as its legs. Key roots: kampē (Ancient Greek: "a bending, a joint").
The door jamb is etymologically the door's leg — from the same root that gives Italian gamba (leg) and the viola da gamba (literally "leg viol," played between the knees). The word gambit in chess also traces here, from Italian gambetto (a tripping of the leg). Even the English word gammon (as in backgammon) may be related. So a door jamb, a chess opening, a cured ham (also from gamba/leg), and a stringed instrument