[n] the mark (') used to indicate the omission of one or more letters from a printed word
[n] address to an absent or imaginary person
Poem which is directly addressed to a person or thing (often absent). An example is Wordsworth's sonnet Milton which begins: 'Milton! thou shouldst be living at this hour'. NB not to be confused with an apostrophe indicating missing letters or the possessive case. Other examples of apostrophe include A Supermarket in California by Allen Ginsberg (addressed to Walt Whitman) and my own poem Invocation.
punctuation, punctuation mark, rhetorical device