Learn Polish: W nocy było pięć stopni. - At night it was five degrees.

In Polish, when you use a number from five onwards (like pięć), the phrase is treated as a quantity. Because of this, the verb describing it must be in the third-person singular neuter form (było), rather than a plural form.

What is the dictionary form of stopni, and why does it look so different here?

The basic word for degree is stopień. Because it comes after the number five (pięć), it must be in the genitive plural case. When making this word plural, the letter e drops out, changing stopień to stopni.

Noc (night) is a feminine word. Why does it end in -y in w nocy?

Noc is a feminine noun, but it belongs to a group of feminine words that end in a consonant rather than an -a. These nouns take the -y ending in the locative case, which is required here after the preposition w.

Is w nocy a set phrase?

Yes, w nocy is a fixed expression meaning at night. You must use the locative case here; you cannot change the ending or omit the preposition without completely changing the meaning.