המכבסה ניקתה את המשי מבלי שהוא דהה.

Because the subject is המכבסה, and מכבסה is a feminine singular noun in Hebrew.

So the verb has to agree with it:

• המכבסה ניקתה = the laundry / laundromat cleaned
• If the subject were masculine singular, you would expect ניקה
• If it were plural, the verb form would change again

In other words, Hebrew verbs in the past tense agree with the subject in gender and number.

מכבסה usually means laundry, laundromat, or laundry service / cleaners, depending on context.

With the ה־ prefix, המכבסה means the laundry or the cleaners.

Even though English might use a business name or an institution without worrying much about grammatical gender, Hebrew treats מכבסה as a regular feminine singular noun, so it takes feminine singular agreement.

את marks a definite direct object.

Here:

• ניקתה = cleaned
• את המשי = the silk as the thing being cleaned

Hebrew uses את before a direct object when that object is definite, such as:

• a noun with ה־ (the)
• a proper name
• a pronoun

So:

• ניקתה את המשי = cleaned the silk
• ניקתה משי = cleaned silk / cleaned some silk

The את does not mean anything by itself in English; it is just a grammatical marker.

Because ה־ is the Hebrew definite article, equivalent to the.

• משי = silk
• המשי = the silk

Since the sentence is talking about a specific piece or batch of silk, Hebrew uses the definite form המשי.

This is also why the direct object marker את appears: את normally goes with a definite direct object.

מבלי means without.

It is very close in meaning to בלי, but מבלי is usually felt to be more formal or more written-style.

So:

• מבלי שהוא דהה = without it fading
• בלי שהוא דהה = also possible in less formal Hebrew

A useful rule of thumb:

• בלי = common, everyday
• מבלי = more formal/literary

Because the fading is being done by the silk, not by the laundry.

In English, you can say:

• without it fading

using a non-finite form (fading). Hebrew often handles this by using a full clause instead:

• מבלי שהוא דהה

Here שהוא means roughly that it.

This helps show clearly that the subject of דהה is המשי, not המכבסה.

A very important point for learners:

• If you used an infinitive after בלי / מבלי, the understood subject is usually the same as the main subject.
• But here the main subject is המכבסה, while the thing that might fade is המשי.
• So Hebrew uses a separate clause with its own subject.

Yes, הוא can mean he, but in Hebrew it also serves as it for masculine singular nouns.

Since משי is a masculine singular noun, Hebrew refers back to it with הוא.

So in this sentence:

• הוא does not mean a male person
• it means it, referring to המשי

Hebrew pronouns follow grammatical gender, not natural gender the way English often does with it.

דהה is the past tense, 3rd person masculine singular form of the verb לדהות = to fade.

It is masculine singular because it agrees with המשי:

• המשי = masculine singular
• therefore: הוא דהה

Compare:

• הבד דהה = the fabric faded
• החולצה דהתה = the shirt faded
  because חולצה is feminine singular

So דהה matches the grammatical gender and number of משי.

Sometimes Hebrew can omit the repeated subject in certain structures, but מבלי שהוא דהה is clearer because it explicitly shows what did not fade.

If you say מבלי שדהה, it may sound more compressed or literary, and some learners may find it harder to parse.

A fully explicit alternative would be:

• מבלי שהמשי דהה

That repeats the noun itself instead of using the pronoun.

So the sentence uses שהוא to keep the reference clear and natural.

Because that would make the subject of to fade seem to be the same as the main subject.

In the main clause, the subject is:

• המכבסה = the laundry

But the thing that would fade is:

• המשי = the silk

If you say מבלי לדהות, Hebrew would normally suggest the laundry is the one not fading, which makes no sense.

So Hebrew needs a separate clause with its own subject:

• מבלי שהוא דהה

This is one of the big differences from English: English often uses without + -ing, but Hebrew often needs a full subordinate clause when the subject changes.

Yes, it sounds somewhat formal or written, mostly because of מבלי and the overall structure.

A more everyday-style sentence might use בלי instead:

• המכבסה ניקתה את המשי בלי שהוא דהה

That said, the original sentence is perfectly useful for learning because it shows several important grammar points:

• verb agreement
• את with a definite object
• noun gender
• a subordinate clause after מבלי

So it is a good example of standard Hebrew syntax, even if it leans a bit formal.