هذه ليست نزهة فقط، بل اجتماع أيضا.

هذه is the feminine singular word for this.

Arabic demonstratives agree with the gender and number of the thing being referred to. So هذه tells you that the speaker is pointing to something grammatically feminine.

Important: this does not automatically happen just because نزهة is feminine. The demonstrative agrees with the actual referent, which may be an understood word from context, such as الفعالية (the event), الرحلة (the trip), or something similar.

If the thing referred to were masculine, you would use هذا instead.

Because ليست is the feminine singular form of ليس.

Since the subject here is هذه, which is feminine singular, ليس changes to ليست to agree with it.

A quick comparison:

• هذا ليس... = this is not... (masculine)
• هذه ليست... = this is not... (feminine)

In this sentence, ليست means is not.

Arabic usually has no present-tense verb to be in simple sentences, so:

• هذه نزهة = this is a picnic / outing
• هذه ليست نزهة = this is not a picnic / outing

So ليس is a very common way to negate a nominal sentence in the present.

Yes, in a sense.

In present-tense Arabic, the verb to be is usually not stated in simple sentences. So Arabic says:

• هذه نزهة literally: this picnic
• natural English: This is a picnic

When you negate that idea, Arabic uses ليس / ليست:

• هذه ليست نزهة = This is not a picnic

In the second half, Arabic also omits repeated material. So بل اجتماع أيضا is short for something like:

• بل هي اجتماع أيضًا = but it is also a meeting

Because the meaning is not just a picnic, but also a meeting.

In Arabic, an indefinite noun often corresponds to English a/an:

• نزهة = a picnic / an outing
• اجتماع = a meeting

If you added ال, the meaning would change:

• النزهة = the picnic
• الاجتماع = the meeting

That would sound more like you are talking about specific known things, not classifying what this is.

فقط means only / just.

Arabic often places فقط after the word or phrase it limits. So:

• نزهة فقط = only a picnic / just a picnic

That is why:

• ليست نزهة فقط = it is not just a picnic

This placement is very natural in Arabic.

بل is used to correct or replace the first idea with a stronger or more accurate one.

So:

• ليست نزهة فقط، بل اجتماع أيضا = It is not just a picnic; rather, it is also a meeting.

لكن usually means but/however and often introduces a separate clause. بل is especially good when the speaker is revising the first description and giving the more accurate one.

So in this sentence, بل is the more natural choice.

أيضا means also / too.

In this sentence, it comes after اجتماع:

• بل اجتماع أيضا = but also a meeting

That placement is very normal. Arabic often puts أيضا after the thing being added.

You may also see slightly different word orders in Arabic, such as:

• بل أيضًا اجتماع
• بل هو أيضًا اجتماع

But the version in your sentence is simple and natural.

Yes. Arabic often omits words that are easy to understand from context.

The full idea is something like:

• بل هي اجتماع أيضًا = but it is also a meeting

The subject is not repeated because it is already clear from the first part of the sentence. This kind of omission is very common and natural in Arabic.

A practical classroom pronunciation is:

hādhihi laysat nuzhatan faqaṭ, bal ijtimāʿan ayḍan

A rough sound guide:

• هذه = hā-dhi-hi
• ليست = lay-sat
• نزهة = nuz-ha
• فقط = fa-qat
• بل = bal
• اجتماع = ij-ti-māʿ
• أيضا = ay-dan

In normal Arabic writing, short vowels are usually not written, so learners often need to know the pronunciation separately.

In ordinary Arabic writing, short vowels and case endings are usually omitted, so you see:

هذه ليست نزهة فقط، بل اجتماع أيضا

In careful fully vocalized Arabic, the first predicate after ليست would normally be:

• نزهةً

So you may see or learn:

• هذه ليست نزهةً فقط...

For the second part, Arabic is being elliptical. If you expand it to:

• بل هي اجتماعٌ أيضًا

then اجتماعٌ would be nominative in that full clause.

Because normal print leaves these endings unwritten, learners usually focus first on the sentence pattern and meaning.

Yes, very much.

This sentence teaches a very useful pattern:

• ليس/ليست ... فقط، بل ... أيضًا = not only / not just ..., but also ...

So you can make similar sentences, for example:

• هذا ليس درسًا فقط، بل مراجعة أيضًا = This is not just a lesson, but also a review.
• هذه ليست رحلة فقط، بل تجربة أيضًا = This is not just a trip, but also an experience.

Another common variation is using مجرد:

• هذه ليست مجرد نزهة، بل اجتماع أيضًا = This is not merely a picnic/outing, but also a meeting.

Both patterns are useful and natural.