Defining words

In the last class we discussed how if a person does not know the definition of something then you can never fulfill that said thing (e.i., If someone does not know the definition of good then he can never do good.) I would like to make a point saying that the defintion of good is

–adjective

1.

morally excellent; virtuous; righteous; pious: a good man.

2.

satisfactory in quality, quantity, or degree: a good teacher;good health.

3.

of high quality; excellent.

4.

right; proper; fit: It is good that you are here. Hiscredentials are good.

5.

well-behaved: a good child."

http://dictionary.reference.com/browse/good

I know the definition of good, so there for I will always do good, according to Socrates and last class.

Furthermore, what if i did not know the definition of "brother" could I ever be a brother? Well clearly i am a brother because I have two male siblings, the point is when does this "way of thinking" become extreme. Just because I do not know the "correct" definition of a word (emphasis on "the"" does that make me incapable of fulfilling that word (good, bad, smart, tall, etc.)

Socrates and his thoughts on definitions is ridiculous. If you asked a person who could not understand any language what is a human and they couldn't tell you, does that make them not a human?

Where is the line drawn.