The word "excise" presents a fascinating case of two etymologically unrelated words that have converged into identical written forms in English. The tax sense and the surgical sense have entirely different origins, making "excise" a homograph — two words that look the same but have distinct histories and meanings.
The tax sense of "excise" entered English in 1494 from Middle Dutch excijs (a tax, a duty), which probably derived from Old French assise (a sitting, a judicial assessment, a tax — from the practice of sitting to assess taxes). The Old French word came from Latin assidere (to sit beside, to assist in judging), combining ad- (to, beside) with sedere (to sit). An excise tax is, at its etymological root, a tax that was "sat upon" — assessed by officials sitting in judgment of goods and their values.
The surgical sense — to excise, meaning to cut out — appeared in English in the 1570s, borrowed directly from Latin excisus, the past participle of excidere (to cut out), from ex- (out) with caedere (to cut). This root also produced "incision" (a cutting into), "precise" (cut cleanly, exact), "decide" (to cut off alternatives), and "concise" (cut short). The Latin caedere was remarkably productive: "caesarean" (a surgical cutting), "scissors" (cutting instruments), and even "cement" (from caementum, rough-cut stone) all descend from it.
The convergence of these two words in English spelling is accidental. They are pronounced slightly differently — the tax is /ˈɛk.saɪz/ (noun, stressed on the first syllable), while the surgical verb is /ɪkˈsaɪz/ (stressed on the second) — but the written forms are identical. This homography has occasionally caused confusion and is a favourite example in linguistics courses on the distinction between homographs, homophones, and homonyms
Samuel Johnson's famous definition of excise (the tax) in his 1755 Dictionary is one of lexicography's most celebrated editorial intrusions: "A hateful tax levied upon commodities, and adjudged not by the common judges of property, but wretches hired by those to whom excise is paid." Johnson was politically opposed to excise taxation, and his definition smuggled polemic into what was supposed to be objective description. The entry provoked complaints but was never amended during Johnson's lifetime.