Tiszta felmosóronggyal mosunk fel.

Because mosunk already contains the subject information.

• mos- = the verb stem wash
• -unk = we in the present tense

So mosunk means we wash.

Hungarian usually leaves out subject pronouns when the verb ending already makes the subject clear. So mi (we) is normally unnecessary unless you want extra emphasis or contrast.

Mos by itself means to wash.

But felmos is a verb with a verbal particle, and it means to mop / to wash the floor. In many Hungarian verbs, particles like fel, le, ki, be, etc. create a new meaning that is not always translated literally.

So here:

• mos = wash
• felmos = mop

The particle fel is historically the same word as up, but in this verb you should learn felmos as a unit of meaning.

Because the sentence is putting emphasis on tiszta felmosóronggyal.

In Hungarian, when a word or phrase is in the focus position right before the finite verb, the verbal particle usually moves after the verb. That is why you get:

• Tiszta felmosóronggyal mosunk fel.

This has a sense like:

• We mop with a clean mop cloth
• or more emphatically, It is with a clean mop cloth that we mop

If there were no special emphasis on the tool, you would more likely expect:

• Tiszta felmosóronggyal felmosunk.

So the split form mosunk fel is mainly about word order and emphasis.

They belong to two different things.

1. In felmosóronggyal, the felmosó- part belongs to the noun compound felmosórongy = mop cloth / floor cloth
2. In mosunk fel, fel is the verbal particle belonging to the verb felmos

So although both contain fel, they are not the same grammatical element in the sentence.

You can think of it like this:

• felmosórongy = a cloth used for mopping
• mosunk fel = we mop

They are related in meaning, but each fel belongs to its own word or construction.

It is the instrumental ending -val / -vel, which often means with.

So:

• felmosórongy = mop cloth
• felmosóronggyal = with a mop cloth

Here it tells you the tool used for the action.

A very common Hungarian pattern is:

• késsel = with a knife
• kanállal = with a spoon
• felmosóronggyal = with a mop cloth

Because the -val / -vel suffix changes after many final consonants.

With this suffix, the v often assimilates to the final consonant of the word, and Hungarian spelling shows that by doubling the consonant.

So:

• rongy + val becomes ronggyal

This is the same pattern as:

• kéz + vel → kézzel
• ház + val → házzal

So ronggyal is the expected form.

Because in Hungarian, when an adjective directly modifies a noun, the case ending normally goes only on the noun, not on the adjective.

So:

• tiszta felmosórongy = clean mop cloth
• tiszta felmosóronggyal = with a clean mop cloth

Not tisztával felmosóronggyal.

This is very normal in Hungarian noun phrases:

• piros autóban = in a red car
• nagy házhoz = to a big house
• tiszta felmosóronggyal = with a clean mop cloth

Because Hungarian often leaves out the article in phrases that express the means or instrument of an action, especially when the noun is indefinite and nonspecific.

So Hungarian very naturally says things like:

• késsel vág = cuts with a knife
• ceruzával ír = writes with a pencil
• tiszta felmosóronggyal mosunk fel = we mop with a clean mop cloth

English usually needs a, but Hungarian often does not in this kind of phrase.

Yes, it is a compound word, and Hungarian makes compounds very freely.

It can be broken down like this:

• felmosó = mopping / mop
• rongy = rag, cloth

So felmosórongy literally means something like mopping cloth or cloth for mopping.

Hungarian often writes such compounds as a single word, where English might use two words or a hyphen.

It can, but it does not have to.

Hungarian can use felmos without stating the object when the meaning is already clear or generic, just like English can say We’re mopping without repeating the floor.

So this sentence simply describes the action and the tool.

If you wanted to add the object, you could say something like:

• Tiszta felmosóronggyal felmossuk a padlót. = We mop the floor with a clean mop cloth.

Notice that with a definite object like a padlót, the verb form can also change to the definite conjugation: felmossuk.