I have a list of words as follows:

```
cat
concatenate
matter
pattern
hat
rather
fathom
at
saturate
vat

```

I need a regular expression to match any words which are a single letter followed by the letters `'at'`.

I currently have `[A-Za-z]at` but that includes the `'cat'` and `'nat'` in `'concatenate'` and the `'rat'` in `'saturate'`. 

How can I make it look for exactly one character before, and make sure that there is not more than 1 character before the 'at'. I tried using {1} but that still didn't work. Thanks for your help.