'가짜' means:
거짓을 참인 것처럼 꾸민 것. (Literally) A lie, untruth, fake disguised as truth.
'진짜' means:
본뜨거나 거짓으로 만들어 낸 것이 아닌 참된 것. (Literally) A real thing that is not copied or fabricated.
'가' in '가짜' uses '假' which is a Chinese character for untruth (lie) or fake and '진' in '진짜' uses '眞' which means truth or verity.
What does '짜' mean in those words? What is its etymology?
'짜' is a pure Korean root word meaning "thing; person."
Other words with '짜':
Maybe 짜 is pure korean word. But its meaning is pretty well explained by Leftium. In most case it mean a thing or person. But the Thing is there is a word 子[자] that exactly means thing or person as well.
연산자[演算子][operator]=연산[operating/calculating]+자[thing] (in math)
인자[因子][factor/a thing that draws another phenomenon]=인[cause]+자[thing]
공자[孔子][Confucius]=공[deep & serious (internally)]+자[person]
일자[日子][time/date]=일[day/sun]+자[thing]
The reason I'm saying this is that, 일자 is spoken like 일짜 for the rule of spelling. So somehow 짜 and 子, I guess, are relevent each other.
I have one more reason for my arguement. I think 8 out of ten korean can guess the meanings closely (I'm Korean) when 짜 is replaced with 子 in some casees above(괴짜, 진짜, 가짜, 퇴짜, 알짜) except for 공자.
