expletive

Concise Oxford English Dictionary © 2008 Oxford University Press:
expletive /ɪkˈspliːtɪv, ɛk-/

▶noun

• 1 an oath or swear word.

• 2 Grammar a word or phrase used to fill out a sentence or a line of verse without adding to the sense.

▶adjective Grammar (of a word or phrase) serving to fill out a sentence or line of verse.

– origin ME (as adj.): from late L. expletivus, from explere ‘fill out’.