c. 1600, "state of mental balance," from Latin aequilibrium "an even balance; a horizontal position," from aequilibris "equal, level, horizontal, evenly balanced," from aequus "equal" (see equal (adj.)) + libra "a balance, pair of scales, plummet" (see Libra). Related: Equilibrious.

"absence or destruction of equilibrium," 1840; see dis- + equilibrium. Specific sense in economics is by 1927.

"in equilibrium from equality of pressure," 1889, from isostasy + -ic.

1590s, "in equilibrium," past-participle adjective from balance (v.). In reference to meal, diet, etc., by 1908.

1570s, "be equal with," from balance (n.). The meaning "serve as a counterpoise to" is from 1590s; that of "bring or keep in equilibrium" is from 1630s; that of "keep oneself in equilibrium" is from 1833. Of accounts, "settle by paying what remains due," from 1580s. Related: Balanced; balancing.

"equilibrium from equality of pressure," 1889 (C.E. Dutton), from iso- + Greek stasis "setting, weighing, standing" (see stasis). Greek isostasios meant "in equipoise with, equivalent to."

"pertaining to the principles of equilibrium of fluids," 1670s, from hydro- "water" + -static "stabilizing" (see -stat). Related: Hydrostatics (1650s); hydrostatical.

by 1812, "pertaining to mechanical forces not in equilibrium, pertaining to force producing motion" (the opposite of static), from French dynamique introduced by German mathematician Gottfried Leibnitz (1646-1716) in 1691 from Greek dynamikos "powerful," from dynamis "power," from dynasthai "to be able, to have power, be strong enough," which is of unknown origin. The figurative sense of "active, potent, effective, energetic" is from 1856 (in Emerson). Related: Dynamically.

mid-14c., "firmness of resolve, mental equilibrium" (of persons), from Old French stablete, establete "firmness, solidity, stability; durability, constancy" (Modern French stabilité), from Latin stabilitatem (nominative stabilitas) "a standing fast, firmness," figuratively "security, steadfastness," from stabilis "steadfast, firm" (see stable (adj.)). In physical sense, "state of being difficult to overthrow, power of remaining upright," it is recorded from early 15c. Meaning "continuance in the same state" is from 1540s.

early 15c., pois, "weight, quality of being heavy," later "significance, importance" (mid-15c.), from Old French pois "weight, balance, consideration" (12c., Modern French poids, with -d- added 16c. on supposed derivation from Latin pondus "weight"), from Medieval Latin pesum "weight," from Latin pensum "something weighted or weighed," (source of Provençal and Catalan pes, Spanish, Portuguese, Italian peso), noun use of neuter past participle of pendere "to hang, cause to hang; weigh" (from PIE root *(s)pen- "to draw, stretch, spin").

Original senses are obsolete. The figurative sense (in reference to abstract things) of "steadiness, balance, equilibrium, composure" is recorded from 1640s, from the sense of "a state of of being equally weighted on either side" (1550s). The meaning "way in which the body is carried" is from 1770.