n. Assimilated form (in Latin, etc.) of in- before r. In the following words, in the etymology, the prefix ir- is usually referred directly to the original in- or in.n. Assimilated form (in Latin, etc.) of in- before r. In the following words, in the etymology, the prefix ir- is usually referred directly to the original in-.n. An abbreviation of Irish.n. In chem., the symbol for iridium.An abbreviation of Ireland.