nothing, nothingness / (Buddhism) mu; the null set: neither yes nor no (in response to a koan or other question that mistakenly assumes an affirmative or negative answer).

chemistry (branch of natural science)

sour / (chemistry) acid

Alternative spelling of 酢 (“vinegar”)

in class

a visit by a student's guardians to observe the class

nothing / nothingness / none / nil / not

non-, un- / non-, un-

transplant rejection / allergic reaction

chain reaction (series of events) / chain reaction (type of nuclear reaction)