The meaning of words change over time. As people tried to understand the Trinity, they had to use words to describe the Trinity. These words came with their own meanings which did not quite fit perfectly when applied to the Trinity. The actual meaning of the word changed once it became used for that aspect of the Trinity. The Trinity is the reality. Words help us express that reality. Here are some examples of these words.
We use the word 'person' to designate the 'threeness' of the Trinity, Father Son and Holy Spirit. But each person is not an individual (since not separate), nor people (also since they are not separate). We use the word 'distinct' to indicate that the Father is not the Son, but again that they are not separate. “The divine persons are really distinct from one another.” (CCC 254) God is used for the whole reality, but particularly for the unity of the Trinity as in there is only one God. Other words for God's unity is substance, essence, being, and existence. We will explore these words more when we explore some philosophy. Each of the attributes of God also express God so we can capitalise them, eg God is Love and God is the Ultimate Reality. God the Father is the origin of the Trinity, but not the start, since 'start' implies time.
We need to use the right words to express the Trinity. The meaning of these words changed over time as their meaning better matched the reality of the Trinity. The correct words are person (threeness), unity, substance, essence, existence, being (oneness) and that each person is distinct. The Father is the origin of the Trinity. Words not to use are individual, separate, people and that the Father 'starts' the Trinity.