tautology

Repetition of the same thing in different words. For example, it is tautologous to say that something is most unique, since unique means that there is only one of its kind and so something cannot be described as ‘more’ or ‘most’ unique; something is either unique or not. Other examples are a new innovation (an innovation is always new); a free gift (all gifts are freely given); a dead corpse (all corpses are by definition dead).

Repetition for effect, however, is not tautologous. It is reasonable to say: ‘There must be no noise; everyone must be silent’. Most expressions of tautology arise from careless use of words. For example, it is tautologous to write: ‘In this essay I am going to write about ...’