Tempo marking, "Molto Rit."

Hi, im a new time composer, and so maybe I'm just uncouth in this particular lane, but isn't there another option of ritardando which is drastically slower (as in slows down the music more tempo markers over less beats). one that is different from a rit and a rall? maybe I'm just not familiar in what rall and rit means, but I'm sure this could be a good option to add, along side having added the "a tempo" marking (which I thank you guys for)