If you're using flashcards, you could include minimal context to make sure you're focusing on the right area. For instance, (몸) 팔 and (수) 팔. Otherwise, without context there is no way to tell which flashcard it will be. The best you could do is simply know that 팔 could be arm or eight. PS: What program are you using? For general flashcards, I highly recommend Anki. They have a cellphone app, desktop program, and browser interface that sync together so that you can always have access to your flashcards.

I think Mojave comments are perfect. For examples, 제 팔이 아파요 (My arm hurts, one of both). 일(1), 이(2), 삼(3), 사(4), 오(5), 육(6), 칠(7), 팔(8), 구(9), 십(10), 십일(11), 이십일(21) etc can be used to read a number. 저는 숫자 팔과 사람 몸의 팔이 혼돈스러워요(I'm so confused when I read number 8 or arm in Korean), 그는 팔대 회장입니다(He is the 8th chairman). There are many Korean words having same sound but never mind cuz you can make sense all of them after all later. 눈(eyes[short sound], snow[long sound]), 말(horse[short sound], word[long sound]), please look up a Korean Dictionary, http://krdic.naver.com/ Have a great weekend.

Korean is all about context. You should just know when the word "arm" makes more sense than the word "eight". "I am waving my arm." - "I am waving my eight." ?? A lot of words have multiple meanings 사과 (apple, apology), 다리 (leg, bridge). You just have to pick the right meaning based on context.