Webster's Revised Unabridged Dictionary · 1913

Expletive

Expletive , adjective

[Latin expletivus, from expletus, past participle of explere to fill up; ex out+plere to fill, akin to plenus full: compare French explétif. See Full.]

Filling up; hence, added merely for the purpose of filling up; superfluous.
Expletive imagery. — Hallam
Expletive phrases to plump his speech. — Barrow

Expletive , noun

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