If all you can see is the big body of something, then you'll only get a general idea of what it is. You'll be able to say that it's generally a certain way, but that's about all. You'll get the gist, but no more.

This is a jukugo word, which usually means on'yomi readings from the kanji. Since 大 has two on'yomi readings, here's a mnemonic to help you remember which one to use:

Generally, it's a bad idea to dye your ties (だいたい). The tie police isn't a big fan of it, and you wouldn't wanna get arrested!