What is a word, letter, or syllable not necessary to the sense, but inserted to fill a vacancy; an oath. While explectives their feeble aid to join, And ten low words oft creep in one dull line. Pope called?

expletive — A word, letter, or syllable not necessary to the sense, but inserted to fill a vacancy; an oath. While explectives their feeble aid to join, And ten low words oft creep in one dull line. Pope. (Webster's 1913.)