Timbrið er blautt.

Because -ið is the definite article for a neuter singular noun in Icelandic.

So:

• timbur = timber / wood in a general or indefinite sense
• timbrið = the timber / the wood

Unlike English, Icelandic usually attaches the to the end of the noun instead of writing it as a separate word.

Timbur is a neuter noun. Gender matters because Icelandic adjectives often have to agree with the noun they describe.

Here, blauttur changes form to match timbrið:

• masculine: blautur
• feminine: blaut
• neuter: blautt

Since timbrið is neuter singular, the adjective must be blautt.

Because blautt is the neuter singular form of the adjective blautur (wet).

In this sentence, blautt is a predicate adjective after er (is), and predicate adjectives in Icelandic still agree with the subject.

So:

• drengurinn er blautur = the boy is wet
• stelpan er blaut = the girl is wet
• timbrið er blautt = the timber is wet

Er means is. It is the 3rd person singular present tense form of að vera (to be).

A few common forms are:

• ég er = I am
• þú ert = you are
• hann / hún / það er = he / she / it is
• við erum = we are
• þið eruð = you are
• þeir / þær / þau eru = they are

Here, the subject is singular, so Icelandic uses er.

This is the normal Icelandic sentence pattern:

subject + verb + complement

So:

• Timbrið = subject
• er = verb
• blautt = complement / predicate adjective

It works very much like English The timber is wet.

Yes. That would usually mean wood/timber is wet in a more general or indefinite sense, rather than referring to a specific piece or batch.

Compare:

• Timbur er blautt. = Wood is wet / Timber is wet (general or indefinite)
• Timbrið er blautt. = The wood is wet / The timber is wet (specific)

So the sentence with -ið points to something more specific.

Here it behaves more like a material / mass noun, similar to English wood or timber.

That means it often refers to the substance or material rather than to one individual object. Even so, Icelandic can still make it definite:

• timbur = wood / timber
• timbrið = the wood / the timber

So although it is not usually thought of as one wood, two woods in this kind of sentence, it still follows normal Icelandic grammar for gender, definiteness, and agreement.

It is in the nominative singular.

That is because it is the subject of the sentence, and subjects are usually in the nominative case.

Also, after vera (to be), the predicate adjective normally agrees with the subject, so blautt is also in the matching form.

A rough pronunciation is something like TIM-bri-thith or TIM-brið, though exact Icelandic pronunciation is a bit subtler.

A few points:

• timb- sounds roughly like English timb- in timber
• r is rolled or tapped more than in most English accents
• ð is like the th in this, not the th in thing
• the final -ið is a common definite ending in neuter nouns

So the ð is a soft voiced th sound.

Because Icelandic often expresses the by attaching it to the noun as a suffix.

So instead of a separate word, you usually get endings like:

• masculine: often -inn
• feminine: often -in
• neuter: often -ið

That is why timbur becomes timbrið rather than using a separate word before it.

Yes. Blautur simply means wet, and it can describe:

• people
• clothes
• objects
• materials
• surfaces

So timbrið er blautt is completely natural for saying that the wood/timber is wet.