Sentence:  There is a manner of gracing the notes or accents in reading, as in singing, but which is always at pleasure. This <WSD>grace note</WSD> in music is called "appoggiatura", that is, "supporter", "insinuator". As the quantities of these little notes in music are always taken out of the next note that follows, so it is in speech. Instead of a plain acute accent, thus /, we may use, which corresponds exactly with the small musical <WSD>grace note</WSD>, a little circumflex grave-accute, thus &#9117;; or acute-grave, thus &#9118;; [...] 
Meaning of the word marked with <WSD> tags:  A musical note, indicated on a score in smaller type with or without a slash through it, played to ornament the melody rather than as part of it. Its note value does not count as part of the total time value of the measure it appears in.