Backward

anticuado

(of an idea: outdated)

atrasado

(undeveloped)

desactualizado

(of an idea: outdated)

pasado de moda

(of an idea: outdated)

retrógrado

(in the direction reverse of normal)

retrógrado

(of an idea: outdated)

rezagado

(undeveloped)

subdesarrollado

(undeveloped)

tercermundista

(undeveloped)

trasnochado

(of an idea: outdated)

atrás

(in the direction towards the back)

hacia atrás

(in the direction towards the back)