oxymoron - Conjoining contradictory terms
Many a times we use two contradictory terms together. say for example: deafening silence, busy doing nothing etc.
euphemism - An inoffensive expression that is substituted for one that is considered offensive
Say for example, Physically challenged or Differently abled instead of physically handicapped, mentally challenged instead of mentally retarded, senior citizen instead of oldster etc.
neologism - A newly invented word or phrase
many new words get added up into the english dictionary day by day due to their increasing usage ans not because of any kind of etymological originof being derived from their roots. Typical examples are: bug in a computer program, Googling has become a verb of late, plastic being popularly used instead of the word credit card.