That's idle – i.d.l.e. Both words can actually be used to describe someone who doesn't work very hard, for example “John is really lazy.” or “John is really idle.” Both mean that John's doesn't really work as much as he should do.
However, there are some very subtle differences between the two words which means we can't use them completely interchangeably. For example, “lazy” will always have a negative connotation; it will give us a very negative idea of the person it's being used to describe. So lazy is always seen as a very bad thing.
However, idle can be used in other contexts, still to mean something or someone doesn't work, but without the negative judgement. So for example, if you press print on your computer, you may see a sign which says “Printer idle.” This means that the printer, at the moment, isn't doing anything. Similarly, sometimes factories must close, because there isn't enough work, an so at that point, the factory is idle. Also, the work force, the people are idle.
It's very very important to think about the adjectives you use in particular because very many of them can carry different connotations. For example: cheap and inexpensive. Both mean that something doesn't cost a lot of money. However, in British English, we often use the adjective cheap to describe something that's not of very good quality. So it can sometimes have a negative connotation.
Similarly, you may find two adjectives that mean similar things, but one adjective can be used with a wider range of nouns. So for example wealthy and rich. We can talk about wealthy people or rich people. Both mean people with lots of money.
However, we can also talk about rich food, rich furnishings, meaning very good quality. So here, rich has a slightly different meaning. It's important to remember that it's difficult to find words that are exact synonyms, which can be used interchangeably, in all contexts.