infix comes from Latin infixus, past participle of infigere ('to fasten in'), from in- ('in') + figere ('to fasten, fix'). Morphologically, the prefixed shape matters: the initial element belongs to the recorded formation and helps explain the modern form's surface analysis. In present English, the noun sense is "an affix inserted within a word, or to fix something firmly inside", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as fix, prefix, suffix, and affix, and in derivatives such as infixation and infixed. Its semantic neighborhood includes insert, implant, embed, and instill, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin infigere and Latin figere.