antispast

from The Century Dictionary.

• noun In ancient prosody, a tetrasyllabic foot, in which the first and last syllables are short and the middle syllables long, as Clytēmnēstră. It is a combination of an iambus and a trochee.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Pros.) A foot of four syllables, the first and fourth short, and the second and third long (#).

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A metrical foot composed of an iambus and a trochee