The reason I think the term Zionist is meaningless, and I agree with the way @west didsblue and @Prestwichblue95 have laid out their argument, is that unless you a) ascertain the context of the post containing the word and b) ascertain the intensions of the poster, it's almost impossible to know exactly which precise definition in which they're using the term.
Lots of people do use in the way you describe it, the expansionist, settler ideology, but lots of people also use it as blanket term for Jews in general, but you also have lots of Jewish people who consider themselves Zionists but disagree with the eradication of the Palestinian state/people, and you have Jewish people who consider themselves Zionists and do agree with the eradication of the Palestinian state/people.
If everyone who uses this term means something slightly different to the everyone else, then the term loses its meaning in any kind of serious debate. Saying the Israeli government and the expansionist, settler ideology is probably far clearer, if that's what you're referring to when you say Zionist, and it doesn't result in tedious back and forths about what words mean and arguing over definitions. Because when you say Zionist, and when I say Zionist we probably aren't talking about the same thing. Using clearer language would go a long way in all of us actually hearing each other and then having meaningful discussions.
