Most je sigurniji ujutro nego noću.

Because je is the present-tense form of biti (to be) for he/she/it is.

So:

• Most = the bridge / a bridge
• je = is

Croatian usually needs the verb to be in this kind of sentence, just like English does:

• Most je sigurniji... = The bridge is safer...

You normally cannot omit je here.

Because most is the subject of the sentence, so it stays in the nominative singular.

• most = bridge
• nominative singular: most

In this sentence, the bridge is the thing being described as safer, so nominative is the expected form.

Sigurniji is the comparative form of siguran (safe).

• siguran = safe
• sigurniji = safer

The ending -iji is a common way Croatian forms comparatives with many adjectives.

So:

• Most je siguran. = The bridge is safe.
• Most je sigurniji... = The bridge is safer...

Because the adjective has to agree with most, which is a masculine singular noun.

• most is masculine
• so the comparative adjective is masculine singular too: sigurniji

Compare:

• most → sigurniji
• cesta (road, feminine) → sigurnija
• mjesto (place, neuter) → sigurnije

This is standard adjective agreement in Croatian.

Nego means than in comparisons.

So:

• sigurniji ... nego ... = safer ... than ...

In your sentence:

• ujutro nego noću = in the morning than at night

A very useful pattern is:

• X je + comparative + nego + Y

For example:

• Ovaj put je kraći nego onaj. = This road is shorter than that one.
• Ljeti je toplije nego zimi. = It is warmer in summer than in winter.

Croatian often uses two comparison patterns:

1. comparative + nego + clause/adverb/time expression
2. comparative + od + noun/pronoun in the genitive

In your sentence, we are comparing times:

• ujutro nego noću

So nego is the natural choice.

Typical use of od:

• Most je sigurniji od starog mosta. = The bridge is safer than the old bridge.

Typical use of nego:

• Most je sigurniji ujutro nego noću.

So a simple rule is:

• use od more often before a noun
• use nego more often before another phrase, clause, or adverbial expression

Ujutro is a fixed adverb meaning in the morning.

It is best learned as a whole word:

• ujutro = in the morning

Croatian often uses these fixed time adverbs instead of a preposition + noun phrase.

Other common ones are:

• danas = today
• sutra = tomorrow
• navečer = in the evening
• noću = at night

So in this sentence, ujutro functions as an adverb of time.

Noću means at night or during the night.

This form comes from the noun noć (night) used in an adverbial way. For a learner, the easiest approach is to treat noću as a set expression meaning:

• noću = at night

So the contrast is:

• ujutro = in the morning
• noću = at night

You do not need to build it word by word every time; it is very common as a time adverb.

Croatian does not have articles like English a/an/the.

So most can mean:

• a bridge
• the bridge

Which one is intended depends on context.

In your sentence, English would often say the bridge, but Croatian simply says most.

The given word order is natural and neutral:

• Most je sigurniji ujutro nego noću.

But Croatian word order is more flexible than English. You may see variations for emphasis, for example:

• Ujutro je most sigurniji nego noću.

This puts more focus on ujutro.

Still, the original version is a very normal, straightforward way to say it.

Yes, grammatically Croatian does not mark that distinction with articles.

So Most je sigurniji ujutro nego noću could correspond to:

• The bridge is safer in the morning than at night
• or, in some contexts, A bridge is safer in the morning than at night

In real usage, context usually makes it clear whether a specific bridge is meant.

A helpful rough guide is:

• si-gur-ni-yi

More carefully:

• si as in see
• gur with a rolled or tapped r
• ni
• ji sounding roughly like yi

The j in Croatian is pronounced like English y in yes.

So sigurniji is not pronounced with an English j sound.

Yes. Like siguran, the comparative sigurniji can refer to:

• physical safety: safer
• certainty/confidence/security in a broader sense: more secure

In this sentence, because the subject is most (bridge), the natural meaning is physical safety:

• the bridge is safer in the morning than at night

Context decides the exact nuance.