Where is the leftover water?
Koichi's tweet last night made even the small remainder of his followers very upset.
I’m going on a date tonight. You can heat up some leftovers from lunch to eat for dinner. Love, Mom.
This has the same meaning as the kanji. The little り thrown on there is just a little remainder sticking off the end of the kanji. No need to pay attention to that.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: You're waiting inside. The remainder of your forces are out there, fighting. You don't know who will survive... or if they even will. You have a secret knock (のこ), though, that you use to find out if it's one of the remaining forces outside or the enemy, broken through. You hear a knock. What is it? Is it your men or theirs? Imagine it out, focusing on the knock conversation that happens between you and the remainder.