Cub, Good reply, however I think the point was the word Trinity is not in the Bible, but was defined, and the term coined by a Council of the Catholic Church. “Additions” to the faith, as Protestants would term them are due to poor scholarship. Yes we can find the Term Trinity, or Transubstantiation or the label Sacrament come up later in the history of the Church, but not the concept. What Protestants fail to recognize is that these only become an issue when someone like themselves or other early heretical movements question or deny what has always been held by the Church. It is at that point that they are defined de fide.
An example in the secular world would be the Narcotics laws in the USA. Before Heroin became a major problem there where no laws against it or other narcotics. Does that mean that narcotic analgesics did not exist until the law banning them was inacted, does that mean the narcotics on the list did not have pain killing qualities or had been previously free from addictive qualities. Only a fool would say yes.
Protestants deny Transubstantiation because in part they say that it was not a belief of the Church until as late as the 1500’s. In the usual non-historical blur that they create, they omit that it was not until the 1500’s that Protestantism was created by men who denied among other things the real presence of our Lord for the first time in history. In response, what did the Church do? When the Council of Trent was promulgated those who held and circulated these novel man made traditions such as Luther and Consubsantiation and other Protestants where inivited to the Council, with a guarentee of safe passage to and from, in order to explain their positions. They refused, so the Council based on their writings reviewed them found them lacking in truth condemned them, but did not stop there. In order to uphold the truth which had been preached and taught from the very beginning of the Church in 33AD when founded by Christ, they defined the belief so there would be no question as to what the Church had always believed. The research and prayers that went into the defining of the dogma included a look into what had always been taught based on the Sacred Scriptures and the writings of the Early Fathers, and Saints. The term to define what the belief was and was not was given in order to not confuse the dogma with the errors of the Protestants. Eastern Catholic and Orthodox, who hold to the same beliefs never required a term because in the East they never faced the novel inventions of the Protestants and nobody in the Eastern Churches ever denied that Christ is physically present in the consecrated elements.
Which brings up one minor pesky little point. Most Latin Rite Catholics are either unaware of or forget about our Eastern Rite Catholic Brothers. Eastern Rite Catholics have a different set of rites that surround the Mass, (in the East primarily called the Divine Liturgy) These Catholics are 100% in communion with the Pope, (unlike the Orthodox Churches) and any Catholic in a state of grace may recieve communion or go to confession in their churches. The Scriptures read in the Liturgy follow a different cycle however. I would encourage any Latin Rite Catholic to assist Mass from time to time in an Eastern Catholic parish if they have one near them, to see the true universality of the Church. I myself attend Mass at an Armenian Catholic Church, and sometimes, (when I wake up late) a Coptic Catholic Church, (Coptics are an ancient rite from Egypt) When travelling I sometimes attend Ukranian, Melekite (Jordianian and Syrian Rites) or even the Traditional Latin Mass where it is offered with the permission of the local bishop. All this shows the broad spiritual heritage of the Church even where the ritual developed differently but the Faith remained the same.