Convenient?

What is the difference between:

convenient              and             convenience ?

convenient is an adjective. We can use it in two ways:

1. After a "be" verb

The iPad is convenient.
Pasmo prepaid transport cards are convenient.
"No-wash" rice is convenient.

2. Before a noun

The TX train is a convenient way to get to Tokyo.
The iPad is a convenient device.
9:00am is the most convenient time for me.


So how about "convenience"? Well, it is an easy word, but not so common. That is we don't use it very much, and often it is in written English. That's because it is a noun, but an abstract noun (not a thing we can see and touch). In writing it is quite formal:

Please reply at your earliest possible convenience. =
Please reply as soon as you can. 

Make an appointment at your convenience. =
Make an appointment when it is a good time for you.

Most people make a mistake with the term "convenience store" :)  In this case we have to use a noun + noun. The first noun acts like an adjective. There are some other common examples in this pattern:

computer mouse
dog house
table lamp

So why do we say "convenience store" and not "convenient store"? That is because "convenience store" is the name of a type of store - we use that name for that special kind of store. There are other examples, too:

department store
gasoline stand
petrol station
police station
football club

If you use the adjective, you mean only THAT store is nice for you:

Kumazawa is a convenient store for me to shop at because I often go to Lala Garden Mall. 

By the way, the word "store" is more American English and the word "shop" is more British English.