Add lists to a master list

Hi, i want to add a list to a 'master' list.  I want to use to cons function for this.

masterList = cons(list_3 masterList)

 This works, no problem, only the number of the list to be added is determened by the i in a for loop.

 for( i 1 20
masterList = cons( "list_i" masterList))

  I don't know what function to use that gives the correct return for "list_i"