Ellipsis is the omission from a sentence of words which are normally needed to complete the grammatical construction or meaning. It occurs most often in everyday speech, in expressions such as Told you so (= I told you so) and Sounds fine to me (= It or that sounds fine to me), and also occurs regularly in all kinds of spoken and written English.
E.g.: http://www.youtube.com/watch?v=PNhHGR2udPM
Antithesis is a rhetorical term for the juxtaposition of contrasting ideas in balanced phrases or clauses. Usually it is built up with the help of 4 words: 2 of them - antonyms and other two make antithesis.
E.g.: His coat-sleeves being a great deal too long, and his trousers a great deal too short, he appeared ill at ease in his clothes. (Dickens)
http://grammar.about.com/od/ab/g/antithesis.htm