Defining Personhood

So I asked a pro-choice person this morning is a fetus a human?  To which he responded, "why yes ofcourse, fetus is a stage of human development; however, a fetus is NOT a person."  When he said this my eyebrow rose.  How can a fetus be a human and yet not a person?  Trust me, I spent hours running my mind through every possibility and it is scary no matter how I look at the situation. So first we shall compare the dictionary definitions:

human- noun; a member of any of the races of the species Homo sapiens; a person; man woman, or child.
person- noun;
1. a human being, whether man, woman, or child: The table seats four persons.

2. a human being as distinguished from an animal or a thing.

3. Sociology . an individual human being, especially with reference to his or her social relationships and behavioral patterns as conditioned by the culture.

4. Philosophy . a self-conscious or rational being.

5. the actual self or individual personality of a human being: You ought not to generalize, but to consider the person you are dealing with.

6. the body of a living human being, sometimes including the clothes being worn: He had no money on his person.

7. the body in its external aspect: an attractive person to look at.

8. a character, part, or role, as in a play or story.

9. an individual of distinction or importance.

10. a person not entitled to social recognition or respect.

11. Law . a human being (natural person) or a group of human beings, a corporation, a partnership, an estate, or other legal entity (artificial person or  juristic person) recognized by law as having rights and duties.

So the definition about a human states that a human is a person; however, the definition of a person is far more complicated depending upon who you ask.  For example: in definition #3 with a focus on Sociology it mentions a person as being defined by their behavior and social relationships; however, I am fearful to define a person based on that because if we defined a person based on their social relationships- would an autistic individual or someone who lacks social skills not be a person?

However, the scariest definition is the one defined in Law.  A person is a human being recognized by law as having rights and duties. Since when does law decide who is a human being deserving of rights?  Oh wait, they already do- ever since Roe v. Wade. First of all, this reminds me of the Holocaust when Hitler said the Jews were not people.  How about putting the Native Americans on reservations because they were "savages", does that sound familiar?  Let us remind ourselves that if we allow law makers to decide what is and isn't a person (i.e. what is personhood?).  Then we are allowing the possibility that we may no longer be defined as people too.  Remember, history repeats itself quite often.  So who are we to decide who is and isn't a person?