Learn Hardcore Dutch: Overigens bewaart de ober de kassabon voor ons. - By the way, the waiter keeps the receipt for us.

Dutch main clauses follow the verb-second (V2) rule. Because the adverbial Overigens is placed first, the finite verb (bewaart) must be in second position, so the subject (de ober) comes after it: Overigens | bewaart | de ober | …. Without that fronted adverb, the neutral order would be: De ober bewaart de kassabon voor ons.

Can I use trouwens instead of overigens?

Yes. Trouwens is more conversational; overigens sounds a bit more formal or written. Both mean roughly “by the way/incidentally” in this sentence and are interchangeable here.

Can overigens go elsewhere in the sentence? Do I need a comma after it?

Yes, it can appear mid-sentence:

De ober bewaart overigens de kassabon voor ons.
De ober bewaart de kassabon overigens voor ons.

A comma after initial Overigens is optional and not normally needed: Overigens bewaart … (no comma) is standard.

Why is it bewaart and not bewaar or bewaard?

bewaart = present tense, 3rd person singular (he/she/it keeps): de ober bewaart.
bewaar = present, 1st person singular (I keep) or imperative: ik bewaar.
bewaard = past participle, used with an auxiliary: heeft bewaard (“has kept”).

What nuance does bewaren have compared to other verbs?

Bewaren means “to keep/store/save (so it remains available/undamaged).” In this context, the waiter is holding onto the receipt for you.

houden can mean “keep (retain),” but is broader and can imply not returning it.
bijhouden = keep track of, maintain.
opbergen = put away/store physically, less about safekeeping for someone.

Why is it voor ons and not just ons?

With the meaning “to keep something for someone,” Dutch uses the preposition voor to mark the beneficiary. De ober bewaart ons would mean “the waiter keeps us,” which is not what you want. So you need voor ons.

Can I move voor ons earlier in the sentence?

Yes: Overigens bewaart de ober voor ons de kassabon. That’s fine and adds emphasis to “for us.” The default preference, though, is direct object before prepositional phrase: … de kassabon voor ons.

Why is it de kassabon and not het kassabon? What about bonnetje?

Bon is a de-word, and the compound kassabon inherits that: de kassabon. The diminutive bonnetje is always het (all diminutives take het): het bonnetje.

Is kassabon the same as rekening?

No:

kassabon / bon: the receipt you get after paying.
rekening: the bill/check you ask for to pay.
factuur: an invoice (with details for bookkeeping/companies).
In Belgium you’ll also hear (kassa)ticket.

Is ober gendered, and is it polite?

Ober historically looked masculine, but today it’s widely used for any waiter. Alternatives:

serveerster (female), kelner (more formal/dated), or neutral job terms like bediening (the staff). As a form of address, shouting Ober! can sound rude; better is eye contact with pardon, meneer (sir), or mevrouw (ma’am).

How do you pronounce the tricky parts?

Overigens [ˈoːvərɪɣəns] — the g is a voiced velar fricative [ɣ].
bewaart [bəˈʋaːrt] — Dutch w is [ʋ], between English w and v.
de ober [də ˈoːbər].
de kassabon [də ˈkɑsaˌbɔn].
voor ons [voːr ɔns]; the r links smoothly: voo[r]ons.

Do I really need both articles (de ober de kassabon)?

Yes. Dutch typically requires an article for definite singular nouns in both subject and object positions. You can’t drop the object article here. If it’s indefinite, you’d use een kassabon.

What’s the passive version of this sentence?

Overigens wordt de kassabon voor ons bewaard (door de ober). You can omit door de ober if the agent is irrelevant: Overigens wordt de kassabon voor ons bewaard.

If I replace the object with a pronoun, what happens to word order and which pronoun should I use?

Object pronouns tend to come before other complements:

For a de-word object like de kassabon, a safe choice is the demonstrative die: Overigens bewaart de ober die voor ons.
If you use the diminutive het bonnetje, then the pronoun is het: Overigens bewaart de ober het voor ons. (In casual speech some use clitic ’m for certain de-words, but die is the clearest/neutral option for inanimate de-words.)

How does overigens differ from bovendien?

overigens = “by the way/incidentally,” adding a side remark.
bovendien = “moreover/what’s more,” adds a strengthening argument or an additional main point. In this sentence, bovendien would slightly change the logic and emphasis.

Why is it spelled kassabon with double s?

It’s the compound kassa + bon; kassa has double s, so the compound keeps it: kassabon. Note: kasbon (single s) exists in Dutch but means a financial certificate, not a receipt.