Hundurinn er mjór.

The dog is thin.

Breakdown of Hundurinn er mjór.

• vera: to be
• hundurinn: the dog
• mjór: thin

Questions & Answers about Hundurinn er mjór.

Why does hundurinn end with -inn, and how do you form the definite article in Icelandic?

hundurinn means the dog. In Icelandic the definite article is not a separate word but a suffix. For masculine nouns in the nominative singular you add -inn, for feminine -in, and for neuter -ið. Attach it to the indefinite form of the noun:

• hundur → hundurinn (the dog)
• kona → konan (the woman)
• hús → húsið (the house)

What form is the adjective mjór taking in Hundurinn er mjór, and why doesn’t it change for number or case?

Here mjór is the masculine nominative singular form of “slim.” In predicative position (after a form of vera) adjectives always take the nominative and agree with the subject’s gender, number, and case. Since hundurinn is masculine singular nominative, the adjective remains mjór, which also happens to be its dictionary form.

Why is mjór in the nominative case after er, and how does that relate to the subject?

The verb vera (equivalent to to be) is a copula that links two nominative elements. You use a predicate nominative—never accusative with vera. Thus both hundurinn (the subject) and mjór (the predicate adjective) share the nominative case, agreeing in gender, number, and case.

How do I express A dog is slim without making the sentence definite?

Use the bare noun form without the definite suffix:
Hundur er mjór.
Here hundur is masculine nominative singular indefinite and mjór remains masculine nominative singular.

How would I ask Is the dog slim in Icelandic?

Form a yes/no question by putting the verb first:
Er hundurinn mjór?
Icelandic yes/no questions place the finite verb (er) in first position, then the subject (hundurinn) and the predicate (mjór).

How do I pronounce Hundurinn er mjór?

IPA approximation: [ˈhʏnʏrɪn ˈɛr ˈmjouːr]
Roughly HOON-doo-rin er MYOHR, where u is like German “ü” [ʏ] and ó is a long [ouː]. The double nn indicates a lengthened [nː].

Does the dog's real-life sex (male/female) change the grammar here?

No. Icelandic grammatical gender is fixed by the noun hundur, which is always masculine, regardless of the animal’s biological sex. You always say hundurinn er mjór whether the dog is male or female.

How would I say the slim dog if I wanted the adjective before the noun?

You need the definite form of the adjective as a prefix:
mjóri hundurinn
Strong masculine adjectives in the definite nominative singular take -i (so mjór → mjóri), matching the noun hundurinn. Alternatively, you can use the separate article hinn: hinn mjóri hundurinn.