godan verb, transitive verb
You know the kanji means eat, and you also already know 食べる. So what's the deal with this also meaning to eat?
食う carries a more masculine and coarse tone than 食べる, so it can come off as rough or impolite in certain situations. It also has a wider set of usages, for example in saying that something is eating up time or resources, or saying that you were bitten by a bug. You'll come across more of these, but they're all pretty straightforward, so don't worry!
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You do know that reading, but this uses a different one, so here's a mnemonic to help you:
There's nothing you love to eat more than cookies (く). You could eat them day and night, but watch out, as that might get a little… time-consuming.
I didn't have time to eat lunch.
Oh no, my silk suit is being eaten by bugs!
It was a job that just ate up my time and didn't pay off.