Mr. Simple recently dropped this line after reading revanche: “The Good Word for 9 September 2014 was revanche. Considering its definition, would irredentism (a word of Italian etymology) be an apposite synonym or not? If not, why?”
These two words are near synonyms. Revanchism refers to the desire to regain territory lost to a neighbor or that has gained independence regardless of ethnic or cultural consideration. Ukraine is culturally distinct from Russia today, and only historically ethnically related.
Irredentism (or irridentism) is the uniting of territories culturally or ethnically related to its/their “mother” culture or ethinc nation. An irredentist attack could aggrandize one territory or several areas culturally or ethnically connected to the attacking nation. It was originally an Italian political term (1879), referring to a party which advocated the recovery and union with Italy of all Italian-speaking districts subject to other countries.
So while the meanings of the two words overlap, but I wouldn’t say they were synonymous.