There are multiple synonyms for the phrase "forward back". The simplest one is "back and forth", which is often used to describe a repetitive motion from one direction to the other. Another synonym is "reversal", which implies a turning from one direction to the opposite one. "Flip-flop" is a term used to describe an indecisive or unpredictable shift from one opinion or stance to another. Additionally, the word "oscillation" implies a regular swinging or fluctuating movement, which can be forward and back or side to side. Lastly, "pendulum" refers to a weight suspended from a fixed point, which swings forward and back in a predictable and regular pattern.