L'únic pegat és petit.

Here L' is the definite article el shortened before a vowel.

• el únic becomes l'únic
• This is the masculine singular article, because pegat is masculine singular

So L'únic pegat is literally the only patch.

Catalan often shortens el and la before vowels:

• l'amic = the friend
• l'àvia = the grandmother

In Catalan, adjective position can affect meaning.

Here, únic before the noun means only:

• l'únic pegat = the only patch

If you put únic after the noun, it more often means unique / special / one of a kind:

• un pegat únic = a unique patch

So in this sentence, l'únic pegat is the natural way to say the only patch.

Because they both agree with pegat, which is masculine singular.

• pegat = masculine singular
• únic describes pegat
• petit also describes pegat

So the agreement is:

• masculine singular: únic, petit
• feminine singular: única, petita
• masculine plural: únics, petits
• feminine plural: úniques, petites

For example:

• L'única peça és petita.
• Els únics pegats són petits.

Because petit is a predicate adjective after the verb és.

In Catalan, after ser or estar, adjectives usually appear without an article:

• El cotxe és gran.
• La casa és nova.
• L'únic pegat és petit.

This works much like English:

• The patch is small not
• The patch is the small

So petit is simply the adjective describing the subject.

The accent in és is important because it distinguishes the verb form from other words spelled es.

• és = is (from ser)
• es = usually a pronoun, as in reflexive constructions

So:

• L'únic pegat és petit. = The only patch is small.

The accent also shows the stressed vowel in writing.

Catalan usually uses ser for inherent or defining characteristics, including size:

• és petit = is small

Size is treated as a characteristic, not a temporary state. So ser is the normal choice here.

In many cases:

• ser = what something is like
• estar = how something is situated or feels, often more temporary

So pegat és petit sounds natural, while pegat està petit would not be normal in this context.

Everything that agrees with the noun would change: the article, únic, and petit.

Examples:

• masculine singular: L'únic pegat és petit.
• feminine singular: L'única peça és petita.
• masculine plural: Els únics pegats són petits.
• feminine plural: Les úniques peces són petites.

So Catalan agreement affects:

1. the article
2. the adjective before the noun
3. the verb, if the subject becomes plural
4. the adjective after the verb

A careful approximate pronunciation is:

LOO-nee(k) puh-GAT es puh-TEET

A bit more help by word:

• l'únic: stress on the first syllable of únic
• pegat: stress on the last syllable
• és: like ess
• petit: stress on the last syllable

In IPA, a central Catalan pronunciation is approximately: /ˈlu.nik pəˈɣat es pəˈtit/

A learner should especially notice that:

• únic has stress at the beginning
• pegat and petit are stressed at the end

Grammatically, Catalan allows different word orders in some contexts, but El pegat únic és petit would not normally mean the same thing.

It sounds more like:

• The unique patch is small rather than
• The only patch is small

To express the only patch, L'únic pegat is the natural form.

So if your intended meaning is only, keep únic before the noun.

The sentence follows a very common Catalan pattern:

subject + verb + adjective

Breaking it down:

• L'únic pegat = subject
• és = verb
• petit = adjective describing the subject

So:

• L'únic pegat = the only patch
• és petit = is small

This is a very useful pattern to learn, because you can reuse it easily:

• La casa és gran.
• El llibre és interessant.
• L'únic problema és greu.