in rhetoric, "a figure conjoining words or terms apparently contradictory so as to give point to the statement or expression," 1650s, from Greek oxymōron, noun use of neuter of oxymōros (adj.) "pointedly foolish," from oxys "sharp, pointed" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + mōros "stupid" (see moron). The word itself is an illustration of the thing. Now often used loosely to mean "contradiction in terms." Related: Oxymoronic.
1894 in the biological sense "repetition of parts in living things;" earlier in rhetoric, "synecdoche in which totality is expressed by contrasting parts" (such as high and low, young and old); from Modern Latin merismus, from Greek merismos "a dividing, division, a partition," from merizein "to divide," from meros "a part, a share" (from PIE root *(s)mer- (2) "to get a share of something"). Related: Meristic. Merismatic "dividing by the formation of internal partitions" is attested by 1849.
"formal public speaking; the art of eloquence," 1580s, from Latin (ars) oratoria "oratorical (art)," fem. of oratorius "of speaking or pleading, pertaining to an orator," from ōrare "to speak, pray, plead" (see orator).
Oratory is the art or the act of speaking, or the speech. Rhetoric is the theory of the art of composing discourse in either the spoken or the written form. Elocution is the manner of speaking or the theory of the art of speaking ...: the word is equally applicable to the presentation of one's own or of another's thoughts. [Century Dictionary]
Meaning "ground for belief" is from late 14c.; that of "obviousness" is from 1660s and tacks closely to the sense of evident. Legal senses are from c. 1500, when it began to oust witness. Also "one who furnishes testimony, witness" (1590s); hence turn (State's) evidence.
"change of substance, conversion of one substance into another," 1570s, originally in rhetoric, from Late Latin metastasis "transition," from Greek metastasis "a removing, removal; migration; a changing; change, revolution," from methistanai "to remove, change," from meta, here indicating "change" (see meta-) + histanai "to place, cause to stand," from PIE root *sta- "to stand, make or be firm." A rhetorical term in Late Latin for "a sudden transition in subjects," medical use for "shift of disease from one part of the body to another" dates from 1660s in English. Related: Metastatic.
"roundabout way of speaking; an instance of this," 1530s, from Latin periphrasis "circumlocution," from Greek periphrasis, from periphrazein "speak in a roundabout way," from peri "around, about" (see peri-) + phrazein "to express" (see phrase (n.)).
Periphrasis is also known as circumlocution; but the term periphrasis generally refers to those cases where the figure is used with effect, while "circumlocution" refers to its faulty use. Periphrasis may be defined as naming a thing indirectly by means of some well-known attribute, or characteristic, or attendant circumstance. [James De Mille, "The Elements of Rhetoric," 1878]