As Stoney said, it's determined from context. How can you tell if:
He held a pike
means he held a spear, or a fish?
Also, it's worth noting that the word will has more than the two definitions you mention. In fact, it has six or more, depending on who is counting, and how those definitions are parsed. Collins, for example, lists eight; Oxford lists six.
More importantly, though, unlike pike, the nuances of will word are hard to separate from each other. They overlap. The dictionary may consider these to be separate meanings of the word:
She will keep the faith.
Accidents will happen.
Boys will be boys.
The Hawks will win the championship.
I will live in Italy.
but all of those express some kind of vague inevitability about the future.
Dictionaries will do their duty, providing multiple definitions in hopes of capturing all of a word's nuances in a relatively complete manner. But I wouldn't get too hung up on those differences. If I'm not living in Italy now, then
I will come to live in Italy.
could refer to a resigned inevitability, a determined resoluteness, a yearning willingness, or a bold prediction. All of those are valid interpretations; none of them would be wrong, and all of them are lodged in the realm of the future.