[Rusty]

When you are offered something, but don't want it, you can refuse it. (decline to accept)
When you are asked to do something, but don't want to do it, you can refuse. (decline to participate, express misgivings)

When you are testing something, but it isn't up to standards, you can reject it. (discard - you cannot test and then refuse)

When the meaning matches what appears in parentheses after each sentence above, 'refuse' and 'reject' are usually not interchangeable, at least not in the USA.


'Reject' may be interchangeable with 'refuse' when the meaning is 'refusing something,'
but I would choose to use 'refuse' instead.

'Refuse' can be followed by a full infinitive-I refuse to go-or an object, whereas 'reject' can only be followed by an object (or a gerund (which is a verbal acting as a noun, i.e., going)).


If we do use 'reject' to mean 'refuse,' we may feel the need to use different words (in fact, we must in many cases).
Example:
Let's go to the cemetery at midnight.
-I refuse to go to the cemetery at night.
-I reject that idea.

The dictionary says that 'refuse' and 'reject' are synonyms, but I reject the idea (I refuse to accept that) in most cases because I tend to assign different meanings to the two words and I use them differently. Others may have different opinions.