Hnerrinn hennar var svo sterkur að barnið fór að hlæja.

Hnerri means a sneeze. Hnerrinn means the sneeze.

In Icelandic, a possessed noun is very often made definite as well, so hnerrinn hennar is the normal way to say her sneeze. English uses just the possessive, but Icelandic commonly uses both the definite noun and the possessive pronoun together.

So the structure is roughly:

• hnerri = a sneeze
• hnerrinn = the sneeze
• hnerrinn hennar = her sneeze

The ending -inn is the suffixed definite article.

That is the normal position for third-person possessives like hans, hennar, and þeirra in Icelandic.

So Icelandic usually says:

• hnerrinn hennar = her sneeze
• bíllinn hans = his car

This can feel backwards to an English speaker, because English puts her before the noun. But in Icelandic, hennar after the noun is the usual pattern.

Because it agrees with hnerrinn, which is:

• masculine
• singular
• nominative

Icelandic adjectives must agree with the noun they describe in gender, number, and case.

So here:

• masculine: sterkur
• feminine: sterk
• neuter: sterkt

Also, after vera (to be), predicate adjectives normally appear in the strong form, so hnerrinn var sterkur is correct, not sterki.

This is a very common Icelandic pattern meaning so ... that.

So:

• svo sterkur að ... = so strong that ...

The first part gives the degree, and the að-clause gives the result.

In this sentence, the sneeze was so strong that it caused the child to start laughing.

No. They look the same, but they have different functions.

1. In svo sterkur að barnið fór að hlæja, the first að means that and introduces the result clause.
2. In fór að hlæja, the second að goes with the infinitive hlæja and is part of the verbal construction fara að + infinitive.

So one að is a conjunction, and the other is part of an infinitive construction.

Literally, fór is the past tense of fara, which usually means go. But in the construction fara að + infinitive, it often means begin or start.

So:

• barnið fór að hlæja = the child started laughing / began to laugh

It does not mean the child physically went somewhere in order to laugh.

Because barnið is the definite form:

• barn = a child
• barnið = the child

The ending -ið is the neuter singular definite article attached to the noun.

So the sentence is talking about a specific child, not just any child.

Yes.

• hnerra = to sneeze
• hnerri = a sneeze

So the noun and the verb are directly related, just like to laugh and a laugh are related in English.

Examples:

• Hún hnerraði. = She sneezed.
• Hnerrinn hennar... = Her sneeze...

These combinations are unusual for English speakers.

In modern Icelandic, the h is not usually pronounced as a full separate English-style h before the consonant. Instead, the following sound is devoiced.

A useful rough guide is:

• hn = a breathy n
• hl = a breathy l

So you can approximate:

• hnerrinn ≈ NER-rinn, with a puff of air before the n
• hlæja ≈ LYE-ya, with a puff of air before the l

This is only an approximation, but it is a good starting point for learners.