Hodierna cena non est tam simplex quam cotidianus cibus, sed avia dicit modum servandum esse.

Hodierna is a feminine nominative singular adjective meaning today’s or of today. It agrees with cena (dinner/supper), which is also feminine nominative singular.

So:

• hodierna = feminine nominative singular
• cena = feminine nominative singular

Latin adjectives must agree with the nouns they describe in gender, number, and case.

This is the standard Latin pattern for comparison of equality:

• tam ... quam = as ... as

So:

• tam simplex quam = as simple as
• non est tam simplex quam = is not as simple as

A native English speaker may expect something more like simpler than, but Latin often uses tam ... quam for this kind of comparison.

Also, simplex is a predicate adjective with cena, so it means:

• the dinner is simple

Here it becomes:

• Today’s dinner is not as simple as ...

Because simplex is a third-declension adjective, and many third-declension adjectives do not have separate masculine and feminine nominative singular forms.

So:

• masculine nominative singular: simplex
• feminine nominative singular: simplex
• neuter nominative singular: simplex

Even though it describes cena, which is feminine, simplex still stays simplex.

Cotidianus cibus is nominative singular:

• cotidianus = masculine nominative singular
• cibus = masculine nominative singular

It is nominative because after quam, Latin is really comparing with an understood clause. The full sense is something like:

• Hodierna cena non est tam simplex quam cotidianus cibus [simplex est].

In other words:

• Today’s dinner is not as simple as everyday food is.

So cotidianus cibus is not an object; it is the subject of an implied comparison.

Yes. It is the same word historically. A learner may also notice that Latin often has the spelling quotidianus as well as cotidianus. Both are connected with the idea of daily or everyday.

So cotidianus cibus means:

• daily food
• everyday fare
• ordinary daily meals

Because Latin commonly uses indirect statement after verbs of saying, thinking, knowing, hearing, and so on.

In English we say:

• Grandmother says that ...

Latin often says:

• avia dicit ... esse

This construction is called the accusative-and-infinitive construction:

• the subject of the reported statement goes into the accusative
• the verb of the reported statement goes into the infinitive

So here:

• dicit = she says
• modum servandum esse = that moderation must be observed

Because modum is the accusative singular, and in an indirect statement the subject of the reported clause is put into the accusative.

The direct statement would be:

• modus servandus est = moderation must be observed

But after dicit, it becomes:

• modum servandum esse

So:

• direct: modus servandus est
• indirect after dicit: modum servandum esse

That is why you see modum instead of modus.

This is a gerundive + esse construction, often called the passive periphrastic. It expresses necessity or obligation.

• servandum comes from servare = to preserve, keep, observe
• esse = to be

Together, servandum esse means something like:

• must be observed
• has to be kept
• ought to be preserved

Since servandum agrees with modum, the full phrase means:

• modum servandum esse = that moderation must be observed

Very literally, it is something like:

• that a measure is-to-be-observed

But the natural English is that moderation must be observed or that one should keep moderation.

Modus literally means measure, limit, or proper amount. In many contexts it naturally develops the sense of moderation or self-restraint.

So modum servare is not just to save a measure. It means:

• to keep within limits
• to observe due measure
• to practice moderation

That is why the phrase is often translated idiomatically as to keep moderation or to be moderate.

Yes, the doer is not stated explicitly. Latin often leaves it unstated when the meaning is general.

So modum servandum esse means:

• moderation must be observed
• one must observe moderation

If Latin wanted to say who had the duty, it could add a dative of agent with this construction, for example:

• nobis modus servandus est = we must observe moderation

But in your sentence, the idea is general: grandmother says that moderation should be kept.

By English standards, yes; by Latin standards, not especially. Latin word order is much freer because endings show the grammatical relationships.

A few things stand out:

• Hodierna cena comes first, giving the topic right away: today’s dinner
• sed avia dicit marks the turn: but grandmother says
• modum servandum esse comes at the end, where Latin often places an important or weighty idea

So the order helps emphasis more than basic grammar. Even if some words were rearranged, the sentence would still mean essentially the same thing because the forms show their functions.