react (iou) and VI (as used in expressions) (sh)

react (iou)

react verb. M17.
[from RE- + ACT verb, orig. after medieval Latin react- pa. ppl stem of reagere, formed as RE- + agere do, act.]
verb intrans. Act in return on an agent or influence; produce a reciprocal or responsive effect; Chemistry undergo a reaction (with another substance). M17.
N. Calder Carbohydrate reacts with oxygen.
verb intrans. Respond to a stimulus; undergo a change or show behaviour under some influence. (Foll. by to.) M17.
R. P. Graves Reacting badly to the inoculation. A. T. Ellis She wondered how the gamekeeper would react.
verb intrans. Act in opposition to some force. Foll. by against. M19.
J. Gross The young reacting against..their elders.
verb intrans. Move or tend in a reverse direction; (of share prices) fall after rising. L19.
verb trans. Cause to react chemically or immunologically with or together. M20.
New Scientist Pupils are asked to react magnesium with dilute nitric acid.