英语词源字典 - 在线词源网站

baluster [baluster 词源字典]: baluster: [17] Etymologically, baluster and banister are the same word. Both come ultimately from Greek balāustion ‘pomegranate flower’, which reached English via Latin balaustium, Italian balaustro, and French balustre. The reason for the application of the term to the uprights supporting a staircase handrail is that the lower part of a pomegranate flower has a double curve, inwards at the top and then bulging outwards at the bottom, similar to the design of some early balusters.

A balustrade [17], from Italian balaustrata via French, is a row of balusters. Already by the mid 17th century a transformation of the l to an n had taken place, producing the parallel banister.
=> balustrade, banister[baluster etymology, baluster origin, 英语词源]
button: button: [14] Button comes via Old French bouton from Vulgar Latin *botōne, a word connected with the verb *hottāre ‘thrust’ (from which ultimately English gets butt ‘hit with the head’). The underlying notion contained in button is thus of something which pushes up, thrusts itself outwards, rather like a bud growing on a plant; the fact that the resulting round knob is used for fastening is, from the point of view of the word’s semantic history, secondary. (Inconclusive attempts have in fact been made to link bud with Old French boter, a descendant of Vulgar Latin *bottāre, and from the 15th century the word button has been applied in English to ‘buds’.)
=> butt
turncoat: turncoat: [16] A turncoat is someone who abandons or betrays a group or cause and joins its opponents. The story goes – probably apocryphally – that there was once a Duke of Saxony whose territories abutted those of France. Clearly anxious always to make the right impression, he had a coat made which was blue on one side and white on the other. When he wished to be seen to be supporting the French interest he wore it with the white side outwards, and when he did not, he wore it with the blue side outwards.

Documentation of this tale is lacking, and probably the expression had a much less specific origin (the phrase turn one’s coat for ‘betray one’s loyalties’ is contemporaneous).
extro-: word-forming element meaning "outwards," a variant of extra- by influence of intro-.
varus (n.): foot deformity in which the feet are extroverted, so that the inner ankle rests on the ground, while the sole of the foot is more or less turned outwards, 1800, from Latin varus "bent, bent outwards, turned awry, crooked," specifically "with legs bent inward, knock-kneed," of uncertain origin.
If the original meaning was 'with the legs opened', varus might be compared with vanus and vastus, and reflect *wa-ro- 'going apart, letting go'. In any case, none of the other etymologies proposed seems plausible. [de Vaan]
The use of classical varus and valgus, which denoted deformities of the legs, in modern medicine to describe deformities of the feet, was criticized by learned writers (see "Edinburgh Medical and Surgical Journal," July 1838).
teres: "Either of two muscles passing below the shoulder joint from the scapula to the upper part of the humerus, one ( teres major) drawing the arm towards the body and rotating it inwards, the other ( teres minor) rotating it outwards", Early 18th century: modern Latin, from Latin, literally 'rounded'.