"cover or shield from danger, harm, damage, exposure, trespass, temptation, insult, etc.," early 15c., protecten, from Latin protectus, past participle of protegere "to protect, defend, cover over, cover in front" (source also of French protéger, Old French protecter, Spanish proteger). This is from pro "before" (from PIE root *per- (1) "forward," hence "in front of, before") + tegere "to cover" (from PIE root *(s)teg- "to cover").
Applied with a wide range, both literal and figurative. The sense in political economy, "guard or strengthen against foreign competition by means of tariffs, etc.," is by 1789. Related: Protected; protecting.