Here's the breakdown:
* Back: The prefix meaning "to move in a reverse direction"
* Slide: This comes from the verb "to slide", which is related to the Latin verb "salire" meaning "to leap, jump, or climb".
While "backslide" doesn't directly use the verb "salire", its meaning is related to the concept of slipping backward or regressing, similar to the idea of losing one's footing and sliding back down.