In some school textbooks, before introducing the probability as a number between $0$ and $1$, the words "likely", "More likely", "less likely" etc. are used to indicate the likelihood of an event. Why are these words chosen and not the words "probable", "more probable", "less probable"? Is it intentional to avoid words having common origin with the word "probability"?
Textbooks tend to try to use the language that would be familiar to readers. In natural speech the use of "likely" is much more prevalent than that of "probable". Interestingly, though, according to Google N-Grams, that hasn't always been the case, with "probable" and "likely" starting nearly level in popularity in 1800:
And yes, as you mentioned, as students mature, we can move them towards sentences like: "x has a greater probability than y" more easily from the use of "likely".