A short way of writing a word consisting some the letters in followed by period.?

It sounds like you're describing a common abbreviation technique: using an ellipsis (...) to indicate missing letters.

For example, instead of writing "excellent" you could write "ex...t".

However, it's important to note that using ellipses in this way is generally considered informal and can be confusing. It's usually better to spell out the entire word or use a more standard abbreviation.