Summary: The prefix *contra-* and its variant *counter-* mean "opposite" or "against." For instance, the prefix *contra-* gave rise to the words [*contra*]dict and [*contra*]st, whereas the variant spelling *counter-* gave rise to [*counter*]act and [*counter*]feit. To [*contra*]dict someone is to speak "against" what she is saying, whereas a [*counter*]clockwise direction is "opposite" of the normal way a clock's hands usually run.
