There are **seven general exceptions** in the **2nd declension**. Instead of
ending in **-is,** seven nouns end in **-s** ****.

Essentially, the **nominative singular** is all that **is different**.
According to my grammar book, the genitive singular is _also_ **-s** instead
of **-a** with a consonant palatization change, but every time I go by the
book when I translate into Latvian, my husband corrects me.

So, apparently, it depends on who you talk to and what they think sounds good.
I don't think it's wrong either way and you'll be understood regardless of
which you choose.

The seven nouns are:

  * **akmens** : stone
  * **asmens** : blade
  * **ūdens** : water
  * **rudens** : fall, autumn
  * **zibens** : lightning
  * **mēness** : moon
  * **suns** : dog

Then there's **sals** (salt). It's _technically_ still a 6th declension noun
but it's moving into the 2nd declension where it'll be an exception…. and no
one really knows which one it's actually in.