define parenthesis
1540s ,  words , clauses , etc. inserted into a sentence ,  from Middle French parenthÃ¨se ( 15c. ) , from Late Latin parenthesis  addition of a letter to a syllable in a word ,  from Greek parenthesis , literally  a putting in beside ,  from parentithenai  put in beside ,  from para -  beside  ( see para - ( 1 ) ) + en -  in  + tithenai ...