Any of the characteristics of ancient Greek culture, civilization, principles and ideals, including humanism, reason, the pursuit of knowledge and the arts, moderation and civic responsibility.

(aviation) A small landing place for helicopters, denoted by a large "H".

Of or relating to the period of the Greek culture, history, or art after the death of Alexander the Great (323 B.C.) to the defeat of Cleopatra and Mark Antony by Octavian (31 B.C.)--though this end-point is often debated, and can range from 146BC to 330ADhttps://en.wikipedia.org/wiki/Hellenistic_period.

(slang) Expressing firm disagreement.

(astronomy) The sudden beginning of the burning of helium in the core of stars of intermediate mass or on the surface of an accreting white dwarf.

(physics) nuclear fusion involving helium nuclei.

(archaeology) a method of determining the age of rock that depends on the production of helium during the decay of various radioactive isotopes of uranium and thorium.

(physics, astronomy) the nucleosynthesis process, in stars with temperatures over 10⁸K, in which helium is converted to carbon and then to oxygen, neon and magnesium

(astronomy) A star in which the strength of the helium absorption lines vary periodically; at times appearing to be a helium star.

(astronomy) A star which has lost most or all of its hydrogen, leaving just a core of helium.