Syncope is the omission of one or more sounds from the middle of a word, often to fit meter or rhyme. Poets use it to shorten a word's pronunciation without changing its basic meaning. It is a type of contraction, but unlike apocope, which cuts off the end of a word, syncope removes sounds from the middle.
Example
The heav'nly lamp above the hill
Shines through the dusky, twilight chill.
Related Definitions
[n] (phonology) the loss of sounds in the interior of a word (as in `fo'c'sle' for `forecastle')
[n] a spontaneous loss of consciousness caused by insufficient blood to the brain