Learn Hardcore Swahili: Bibi ni mcheshi nyumbani jioni. - Grandmother is cheerful at home in the evening.

Very commonly it means grandmother.
It can also mean old lady or elderly woman in a respectful way.
In some contexts it can mean lady, madam, or Mrs. (e.g. Bibi Fatma = Mrs Fatma / Lady Fatma).

In this sentence, if the context is family, it will normally be understood as grandmother. Without context, it’s simply the (older) woman / lady that the speaker has in mind.

What is ni doing here? Is it a verb like is?

Ni is the Swahili copula, roughly equivalent to English is / am / are when you link a subject to a noun or adjective:

Bibi ni mcheshi → Grandma is cheerful/funny.

A few points:

Ni does not change for person or number. It’s ni for I, you, he/she, we, they.
It is mainly used in equational sentences: X ni Y (X = Y).
For tenses other than simple present or for more focus on time, you often use the verb kuwa (to be) with tense markers:
- Alikuwa mcheshi = She was cheerful.
- Atakuwa mcheshi = She will be cheerful.

In your sentence, ni is a simple present is.

Why is there no separate word for she in the sentence?

Swahili usually does not use independent subject pronouns (like I, you, she) unless you want to emphasize or contrast something.

Here:

Subject is understood from the noun bibi.
You could technically say Yeye ni mcheshi nyumbani jioni, but that would sound like you’re stressing she (as opposed to someone else).

The normal, neutral way is just:

Bibi ni mcheshi nyumbani jioni.

Is mcheshi an adjective like cheerful, or a noun like a funny person?

Grammatically, mcheshi is a noun of the m‑/wa‑ (class 1/2) type, meaning a humorous / playful / funny person.

However, in English we usually translate it with an adjective (cheerful, funny) because that sounds more natural:

Literal-ish: Bibi ni mcheshi = Grandma is a joker / a humorous person.
Natural English: Grandma is cheerful / funny.

So you can think of mcheshi as a person who tends to joke and laugh a lot. It behaves like a noun in Swahili grammar even though we often use an adjective in English translation.

How is mcheshi formed? Is it related to a verb?

Yes. Mcheshi is derived from the verb -cheka (to laugh) or the related root -chesha (to make someone laugh / to amuse).

The m- prefix is a person marker for noun class 1.
So m‑ + (ch)eshi → mcheshi ≈ a person who causes laughter / is amusing.

Related forms:

Kucheka = to laugh.
Kumchekesha mtu = to make someone laugh.
Wacheshi = funny people / cheerful people (plural of mcheshi).

Why is there no word like at or in before nyumbani?

In Swahili, location is often expressed with a suffix, not a separate preposition.

Nyumba = house.
Nyumbani = at home / in the house / to the house (depending on context).

The ‑ni ending is a locative suffix meaning something like in / at / on. So:

nyumbani already means at home; you don’t add another preposition like kwa, katika, or kwa here.
Saying katika nyumbani is usually unnecessary or odd; nyumbani alone is correct.

What exactly does jioni mean, and is it like in the evening?

Jioni is a time-of-day noun meaning evening / late afternoon.

When you just say jioni in a sentence, it usually translates as in the evening:

Bibi ni mcheshi nyumbani jioni.
→ Grandma is cheerful at home in the evening.

You don’t need a separate preposition like in:

Not katika jioni, just jioni.

Other time-of-day words behave similarly:

asubuhi = in the morning
mchana = in the afternoon / during the day
usiku = at night

Is the word order subject – ni – description – place – time fixed, or can I move things around?

Swahili word order is fairly flexible, especially with adverbials (place and time phrases). The basic neutral order here is:

Bibi (subject) ni (copula) mcheshi (description) nyumbani (place) jioni (time).

You can move nyumbani and jioni for emphasis:

Bibi ni mcheshi jioni nyumbani.
Jioni, bibi ni mcheshi nyumbani.
Nyumbani, bibi ni mcheshi jioni.

All are possible; the meaning stays the same, but you slightly shift what you highlight (e.g. starting with Jioni emphasizes in the evening).

Why is there no word for a or the (like a grandmother, the grandmother)?

Swahili does not have articles like a / an / the. Nouns appear without them:

bibi can mean a grandmother, the grandmother, or grandma depending on context.

If you really need to specify, you use other words:

bibi mmoja = one grandmother (often a grandmother in English).
yule bibi = that grandmother.
bibi huyu = this grandmother.

But normally, context tells you whether English should use a or the.

How would I say Grandma is not cheerful at home in the evening?

To negate ni, you use si:

Bibi si mcheshi nyumbani jioni.
= Grandma is not cheerful at home in the evening.

Notes:

Ni → si is the basic present-tense negative copula.
You don’t need any extra negative marker (like ha‑ or ‑si) for this type of nominal sentence; si alone is enough.

Does this sentence mean right now, this evening, or a general habit?

By default, Bibi ni mcheshi nyumbani jioni suggests a general or typical situation, not just one specific evening:

Roughly: Grandma (tends to be / is usually) cheerful at home in the evenings.

If you want to stress habit, you can add huwa:

Bibi huwa mcheshi nyumbani jioni.
= Grandma is usually/always cheerful at home in the evening.

If you wanted this specific evening, you’d typically add a more specific time word:

Jioni hii, bibi ni mcheshi nyumbani.
= This evening, Grandma is cheerful at home.

Can bibi also mean wife? Would that change this sentence?

In some varieties of Swahili and in older usage, bibi can mean wife or lady (as in my lady). In most everyday modern usage:

bibi = grandmother / old lady
mke = wife

So, Bibi ni mcheshi nyumbani jioni will almost always be heard as Grandma / the old lady is cheerful at home in the evening, not The wife….

If you wanted to clearly say My wife is cheerful at home in the evening, you would more typically say:

Mke wangu ni mcheshi nyumbani jioni.