The Collaborative International Dictionary of English v.0.48:
Tranquilizing \Tran"quil*i`zing\, Tranquillizing \Tran"quil*li`zing\, a. Making tranquil; calming. " The tranquilizing power of time." --Wordsworth. -- Tran"quil*i`zing*ly or Tran"quil*li`zing*ly, adv. [1913 Webster]