Radísan vex hratt.

Because Icelandic usually puts the definite article on the end of the noun instead of using a separate word like the.

• radísa = radish
• radísan = the radish

Here, radísan is the nominative singular definite form.

Yes. Radísa is a feminine noun, and gender matters a lot in Icelandic because it affects articles, adjective forms, and sometimes other parts of the sentence.

For this noun:

• radísa = indefinite singular
• radísan = definite singular

So the feminine gender helps explain why the definite form looks the way it does.

It is in the nominative case because it is the subject of the sentence — the thing doing the action of growing.

In Radísan vex hratt, the radish is the one that grows, so nominative is the expected case.

Vaxa is the dictionary form of the verb, meaning to grow.
Vex is its 3rd person singular present form, used with a singular subject like radísan.

So:

• að vaxa = to grow
• ég vex = I grow
• þú vex(t) = you grow
• hann / hún / það vex = he / she / it grows

This verb is a bit irregular, so the present-tense form does not look exactly like the infinitive.

Because Icelandic often uses the simple present where English might use either grows or is growing, depending on context.

So Radísan vex hratt can naturally mean:

• The radish grows quickly
• or, in some contexts, The radish is growing quickly

Icelandic does have ways to express ongoing action more explicitly, but the simple present is very common and often enough on its own.

Hratt is an adverb, meaning quickly / fast.

It describes how the radish grows.

A useful thing to know is that many Icelandic adverbs are identical to the neuter singular form of an adjective. Here, hratt is related to the adjective hraður = fast, quick.

So:

• hraður = fast, quick
• hratt = quickly, fast

Yes, this is a very normal word order:

• Radísan = subject
• vex = verb
• hratt = adverb

So it follows a basic subject–verb–adverb pattern.

Icelandic does allow other word orders in some contexts, but this sentence is straightforward and natural.

Yes. In English, adverbs like fast and quickly can overlap, and hratt works similarly.

So depending on context, it could be translated as:

• quickly
• fast

In this sentence, both are reasonable in English.

Vex is pronounced approximately like vehks.

A rough guide:

• ve- like ve in very, but shorter
• -x like ks

So the whole word sounds close to vehks.

A rough English-friendly approximation is rah-DEE-san.

Very roughly:

• ra- = rah
• dí = dee
• san = san

The stress in Icelandic usually falls on the first syllable, so the first part gets the main stress, even if the long vowel in dí is very noticeable.