mid-15c., "that points out, states, or declares" (grammatical), from Old French indicatif (14c.), from Late Latin indicativus "serving to point out," from indicat-, past participle stem of Latin indicare "to point out, show" (see indication). The "mood in the conjugation of a Latin verb whose essential function is to state a fact (as opposed to a wish, supposition or command)" [The Middle English Compendium]. Related: Indicatively.
late 14c., disposicioun, "ordering, management, a setting in order, arrangement," also "tendency of mind, aptitude, inclination," from Old French disposicion (12c.) "arrangement, order; mood, state of mind" and directly from Latin dispositionem (nominative dispositio) "arrangement, management," noun of action from past-participle stem of disponere "to put in order, arrange" (see dispose).
Meaning "frame of mind, attitude, inclination; temperament, natural tendency or constitution of the mind" (late 14c.) are from astrological use of the word for "position of a planet as a determining influence" (late 14c.). Related: Dispositional.
mid-15c., optatif, "the optative mood," in grammar, a form of a verb expressing wish or desire, from Old French optatif (15c.), from Late Latin optativus, from Latin optatus "wished, desired, longed for," past participle of optare "to choose, wish, desire" (see option). Also mid-15c. as an adjective, "expressing wish or desire by a distinct grammatical form." The general adjectival sense of "expressing or expressive of desire or wish" is by 1610s.
"pertaining to or affected by a mode," 1560s, originally a term in logic, from French modal and directly from Medieval Latin modalis "of or pertaining to a mode," from Latin modus "measure, extent, quantity; proper measure, rhythm, song; a way, manner, fashion, style" (in Late Latin also "mood" in grammar and logic), from PIE root *med- "take appropriate measures." Musical sense is from 1590s; In grammar from 1798.
"with a positive mood," 1947, apparently from on the upbeat "improving, getting better," attested from 1934 and a favorite of Billboard magazine headline-writers in the early 1940s, from the musical noun upbeat (1869), referring to the beat of a bar at which the conductor's baton is in a raised position; from up (adv.) + beat (n.). The "optimistic" sense apparently for no other reason than that it sounds like a happy word (the musical upbeat is no more inherently "positive" than any other beat).
Middle English pal, from Old English pæll "rich cloth or cloak, purple robe, altar cloth," from Latin pallium "cloak, coverlet, covering," in Tertullian, the garment worn by Christians instead of the Roman toga; related to pallo "robe, cloak," palla "long upper garment of Roman women," perhaps from the root of pellis "skin." The notion of "cloth spread over a coffin" (mid-15c.) led to figurative sense of "dark, gloomy mood" (1742). The earlier figurative sense is "something that covers or conceals" (mid-15c.).