The apostrophe ( ’ or ‘ ) is a punctuation mark, and sometimes a diacritical mark, in languages that use the Latin alphabet or certain other alphabets. In English, it serves three purposes: The marking of the omission of one or more letters (as in the contraction of do not to don’t). The marking of possessive case (as in the eagle’s feathers, or in one month’s time). The marking by some as plural of written items that are not words established in English orthography (as in P’s and Q’s). Apostrophe comes ultimately from Greek (, “[the accent of] ‘turning away’, or elision”), through Latin and French. The apostrophe looks the same as a closing single quotation mark, although they have different meanings. The apostrophe also looks similar to, but is not the same as, the prime symbol ( ′ ), which is used to indicate measurement in feet or arcminutes, as well as for various mathematical purposes, and the ʻokina ( ), which represents a glottal stop in Polynesian languages. Such incorrect substitutes as ´ (acute) and ` (grave) are common in unprofessional texts, where an ambiguous treatment of the apostrophe in digital typesetting (as explained below) is a major factor of this confusion.