abscisic,a.Biochem.|æbˈsɪsɪk|[f.abscisin + -ic.]abscisic acid: a plant hormone, C₁₅H₂₀O₄, which promotes seed and bud dormancy and inhibits germination.1968F. T. Addicottet al. in Science 29 Mar. 1493/3Abscisin II was the name given to the second of two abscission-accelerating substances isolated from cotton fruit... Some confusion has developed from the use of the two names, abscisin II and dormin... We now propose the term abscisic acid.1969New Scientist 10 Apr. 71/1Abscisic acid..is now believed to be the principal plant hormone controlling dormancy.1978Sci.Amer.Aug. 75/3Sprouting of the seeds within the ripe fruit, for which the temperature and moisture conditions are ideal, is inhibited by abscisic acid and unidentified substances that are normally present.1978Nature 12 Oct. 571/2The known and accepted hormonal regulators of plant growth and development comprise the auxins, the gibberellins, the cytokinins, abscisic acid and (perhaps) ethylene.