intensifier

That which intensifies.

A word or particle that heightens the intensity of meaning of a term.

“Plus-” and “doubleplus-” are both intensifiers that replace words of different extremities, and the words very and extremely respectively. So words like great, excellent and horrible are rendered redundant in Newspeak, replaced by “plusgood”, “doubleplusgood” and “doubleplusungood” respectively. Note how “un-” has to follow the intensifier prefix.

A chemical agent used to intensify the lights or shadows of a photograph.