untie; unravel; undo (a fastening); unwrap / dispel (doubts); clear up (a matter)

solve (a problem); answer (a question); unravel (a riddle) / comb; untangle (hair)

(algebra) variable / (computing) variable

need, necessity

needed, necessary

mathematics (field of study)

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

Alternative spelling of ワイシャツ (“button-down shirt”)

y-axis (axis on a graph that is usually drawn from bottom to top)

X-ray (short wavelength electromagnetic radiation) / X-ray (photograph made with X-rays)