Turn of phrase
A particular arrangement of words, as in I'd never heard that turn of phrase before, or An idiom can be described as a turn of phrase. This idiom alludes to the turning or shaping of objects (as on a lathe), a usage dating from the late 1600s.
2 ((the 〜))紫の布；（特にもと高位高官者が着用した）紫衣.
3 枢機卿(けい)の地位［職務］；司教［主教］の地位［職務］；((the 〜))帝位, 王位, 王子の地位；高官の地位.
be born to ［in］ the purple((文))帝王［王侯貴族］の家に生まれる；非常な特権階級にある.
━━[形]（more 〜, most 〜；時に-pler, -plest）
turn ［go］ purple with anger
2 帝王の, 国王の；王侯の.
3 華麗な, 豪華な；〈文体が〉（そこだけが目立って）美文調の, 華麗な
a purple passage ［patch］
4 感傷的でオーバーな, きわどい.
［古英語purpure. 2番目の-r-は異化により-l-に変わった. ⇒MARBLE］
purple patch, an over‐written passage in which the writer has strained too hard to achieve an impressive effect, by elaborate figures or other means. The phrase (Latin, purpureus pannus) was first used by the Roman poet Horace in his Ars Poetica (c.20 BCE) to denote an irrelevant and excessively ornate passage; the sense of irrelevance is normally absent in modern usage, although such passages are usually incongruous. By extension, ‘purple prose’ is lavishly figurative, rhythmic, or otherwise overwrought. See also bombast, fustian.