Enthalpy: (symbolized H, also called heat content) is the sum of the internal energy of matter and the product of its volume multiplied by the pressure. Enthalpy is a quantifiable state function, and the total enthalpy of a system cannot be measured directly; the enthalpy change of a system is measured instead. Enthalpy is a thermodynamic potential, and is useful particularly for nearly-constant pressure process, where any energy input to the system must go into internal energy or the mechanical work of expanding the system.
(sense 1): Interjection signifying pain, weariness, disgust, resignation, etc. Very often part of oy vey or oy vas mir. Compare to English Jeez. (from Yiddish "oy", probably from old German; probably cognate to English "oh").
(sense 2): Interjection signifying annoyance. Very similar to sense 1, but more annoyed than resigned. (Probably from Cockney accent of English "Hey".)
(sense 3) Greeting meaning "hello" or "Hi". (Probably from Cockney "hi").(sense 1) Oy, my feet hurt.
(sense 2) Oy! What the 'ell do ya think you're doin'?