Unavoidable, inevitable. This rare word tends to be used to refer to major things, such as an ineluctable fate. A related word of opposite meaning, even more rare, is eluctate, meaning to struggle your way out from something. If you're taking an English literature class in college, you might discover that the novel Ulysses by James Joyce is ineluctable. In that book, the third chapter begins with the sentence: "Ineluctable modality of the visible: at least that if no more, thought through my eyes." You might want to switch majors.
(Will be published in the July 2009 issue of Denver's Community News.)
I'm collecting all of these at: http://www.dvorkin.com/davidsdefs.html