صديقي ضد القرار.

Because Arabic usually leaves out the present-tense to be.

So صديقي ضد القرار literally looks like my friend against the decision, but in natural English it means My friend is against the decision.

If you wanted a different tense, then Arabic would usually use a verb:

• كان صديقي ضد القرار = My friend was against the decision
• سيكون صديقي ضد القرار = My friend will be against the decision

صديقي means my friend.

It is made from:

• صديق = friend
• ـي = my

So the ـي is a possessive suffix attached directly to the noun.

A few useful comparisons:

• صديقٌ = a friend
• الصديقُ = the friend
• صديقي = my friend

Because Arabic usually does not put الـ on a noun that already has a possessive suffix.

So:

• صديقي already means my friend
• adding الـ would be wrong here

The possessive suffix already makes the noun definite. In other words, my friend is already specific, so Arabic does not also add the.

Here ضد means against or opposed to.

For a learner, the easiest way to think of it is as a preposition-like word:

• ضد القرار = against the decision

A more advanced note: in traditional grammar, ضد is often treated as a noun used in a preposition-like/adverbial way, which is why fully vowelled texts may show it as ضِدَّ.

No. You say:

• ضد القرار

not:

• ضد للقرار

So ضد is followed directly by the noun phrase.

This is different from some other expressions, such as:

• معارضٌ لِلقرار = opposed to the decision

That expression uses لِـ, but ضد does not.

Because القرار means the decision, not a decision.

The prefix الـ is the Arabic definite article, equivalent to the.

So:

• قرار = a decision / decision
• القرار = the decision

It is pronounced al-qarār.

Here the ل does not disappear, because ق is a moon letter, not a sun letter.

So you pronounce the article clearly:

• القرار = al-qarār

Compare that with a sun-letter word like الشمس, where the ل is not pronounced separately.

A common pronunciation guide is:

ṣadīqī ḍidda al-qarār

A rough English-style approximation would be:

sa-DEE-qee DID-da al-qa-RAAR

A few sounds to notice:

• ص in صديقي is an emphatic s
• ض in ضد is an emphatic d
• ق in القرار is q, pronounced farther back than English k
• ي at the end of صديقي is a long ee sound

In fully vowelled MSA, you may see:

صَديقي ضِدَّ القَرارِ

A simple explanation:

• صديقي is the topic/subject of the sentence
• ضد القرار is the predicate
• القرارِ has a genitive ending in full vocalization

Also, the nominative ending on صديقي is not heard in the normal way because the noun is attached to the suffix ـي.

In ordinary Arabic writing, these short vowels are usually not written, so you normally just see:

صديقي ضد القرار

Yes. This is a very normal Arabic nominal sentence pattern:

• صديقي = topic/subject
• ضد القرار = comment/predicate

So the structure is basically:

My friend + against the decision

You could change the order for emphasis in some contexts, but صديقي ضد القرار is the neutral, straightforward version.

Yes. A few common alternatives are:

• صديقي يعارض القرار = My friend opposes the decision
• صديقي معارضٌ للقرار = My friend is opposed to the decision

The original sentence, صديقي ضد القرار, is short, clear, and perfectly natural in MSA.