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Examples: Huset er stort. 'The house is big.'
Vinduet er åpent. 'The window is open.'

Note how the :

• The definite article (the) goes at the end and that the t in huset etc. is not pronounced.
• Adjectives referring back to singular neuter nouns usually end in -t.

Feminine nouns

Most feminine nouns can also be used as masculine nouns, but not vice versa.  For these words we use the term 'common gender'.  You can say: ei dame 'a lady' - dama 'the lady', or: en dame - damen.

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However, there are common gender words that almost exclusively takes take the feminine form (ei in the singular Indefinite and -a in the singular Definite): 
jente 'girl', kjerring 'old woman (derogatory)', hytte 'hut/cabin/simmer summer house', bikkje 'dog', geit 'goat', ku 'cow', høne 'hen', gate 'street', bygd 'village/settlement', li 'hillside', myr 'bog', mark, meadow, øy 'island'

Plurals

The main rules are:

Indefinite plural

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To form the Indefinite plural add -(e)r to masculine (-en words) and to feminine (-a words) and to neuter .nouns:

Katter (cats),  gutter (boys),  jenter (girls), vinduer (windows)

Nouns ending in er only take -e in the Indefinite plural, e.g. en lærer - læreren - lærere.

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Huset har fire vinduer. 'The house has four windows.' (neuter)

Han har to hus. 'He has two houses (one syllable neuter word)

Han drakk to glass øl.' He drank two glasses of beer.' (one syllable neuter word)

Definite plural 'e.g. bilene the cars'

Kattene (the cats),  guttene (the boys),  jentene (the girls), vinduene (the windows)

To form the Definite plural add -(e)ne to masculine (-en words), feminine (-a words) and neuterneuter (-et words) Definite singulars.

Bilene står utenfor huset. 'The cars are (lit. 'standing') outside the house.' (masculine)

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Neuter nouns have a choice in the Definite plural between -ene and -a. As in common gender words the -a form is the more conservative and colloquial.  Husene er pene 'The houses are nice.' conservative/literary

Husene er pene. 'The houses are nice.' (conservative/literary)

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Jeg har mange dyr. 'I have many animals.'

Han har to hus. 'He has two houses (one syllable neuter word)

Han drakk to glass øl. 'He drank two glasses of beer.' (one syllable neuter word)

Neuter compound words where the last element is a monosyllabic neuter word follow the rule of monosyllabic neuter nouns e.g. et armbånd, arm+bånd (bracelet), et kjøleskap kjøle+skap (fridge/ literally cool cupboard, etc.

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