terrific (adj.)

c. 1400, "causing terror; that excites or is fitted to excite awe or dread; frightful; unendurable," from Old French terrible (12c.) and directly from Latin terribilis "frightful," from terrere "fill with fear."

This is reconstructed to be from PIE root *tros- "to make afraid" (source also of Sanskrit trasanti "to tremble, be afraid," Avestan tarshta "scared, afraid," Greek treëin "to tremble, be afraid," Lithuanian trišėti "to tremble, shiver," Old Church Slavonic treso "I shake," Middle Irish tarrach "timid").

Also used in reference to the sources of feelings akin to dread, hence, by 1590s, "violently severe" etc., weakening by 18c. to a mere intensive, "great, severe" (a terrible bore; compare similar evolution in awful, terrific, etc.). Frequently applied to misbehaving children (terrible twos is attested by 1949), then to adults. By 1913, colloquially, terrible had the sense of "very bad; extremely incompetent."

"make afraid, fill with fear and alarm," 1570s, from Latin terrificare "to frighten, make afraid," from terrificus "causing terror" (see terrific).

Related: Terrified; terrifying; terrifyingly; terrification (1610s). Terriblize "become terrible" (c. 1600) did not survive but seems to have left no other single word for that.

*dhē-, Proto-Indo-European root meaning "to set, put."

It forms all or part of: abdomen; abscond; affair; affect (v.1) "make a mental impression on;" affect (v.2) "make a pretense of;" affection; amplify; anathema; antithesis; apothecary; artifact; artifice; beatific; benefice; beneficence; beneficial; benefit; bibliothec; bodega; boutique; certify; chafe; chauffeur; comfit; condiment; confection; confetti; counterfeit; deed; deem; deface; defeasance; defeat; defect; deficient; difficulty; dignify; discomfit; do (v.); doom; -dom; duma; edifice; edify; efface; effect; efficacious; efficient; epithet; facade; face; facet; facial; -facient; facile; facilitate; facsimile; fact; faction (n.1) "political party;" -faction; factitious; factitive; factor; factory; factotum; faculty; fashion; feasible; feat; feature; feckless; fetish; -fic; fordo; forfeit; -fy; gratify; hacienda; hypothecate; hypothesis; incondite; indeed; infect; justify; malefactor; malfeasance; manufacture; metathesis; misfeasance; modify; mollify; multifarious; notify; nullify; office; officinal; omnifarious; orifice; parenthesis; perfect; petrify; pluperfect; pontifex; prefect; prima facie; proficient; profit; prosthesis; prothesis; purdah; putrefy; qualify; rarefy; recondite; rectify; refectory; sacrifice; salmagundi; samadhi; satisfy; sconce; suffice; sufficient; surface; surfeit; synthesis; tay; ticking (n.); theco-; thematic; theme; thesis; verify.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dadhati "puts, places;" Avestan dadaiti "he puts;" Old Persian ada "he made;" Hittite dai- "to place;" Greek tithenai "to put, set, place;" Latin facere "to make, do; perform; bring about;" Lithuanian dėti "to put;" Polish dziać się "to be happening;" Russian delat' "to do;" Old High German tuon, German tun, Old English don "to do."