Elision: The omission of part of a word (typically a letter). Elision most commonly involves replacing a word-ending vowel with an apostrophe when it is followed by another word that begins with a vowel. Elision is often employed to make verse more rhythmic or to conform to a metrical pattern but may also be used in prose.
EXAMPLES: E’er, o’er. The line in John Milton’s Paradise Lost (1667) in which the angel Michael tells Adam “All th’earth he gave thee to possess and rule” involves the omission of the first of two adjacent vowels.