Cheville is
the French word for a plug, applied to any word or phrase of little semantic
importance which is used by a poet to make up the required number of syllables
in a metrical verse line. Chaucer used chevilles with shameless frequency,
often plugging his lines with 'eek', 'for sothe', 'ywis', 'I gesse', T trowe',
and similar interjections.