There are many synonyms for "particular", depending on the specific context. Here are a few options, categorized by their nuance:

Specific:

* Specific

* Precise

* Exact

* Definite

* Explicit

* Detailed

Unique:

* Unique

* Peculiar

* Distinctive

* Individual

* Special

* Unusual

Fussy:

* Finicky

* Fussy

* Demanding

* Difficult

* Selective

* Prone to nitpicking

Important:

* Important

* Crucial

* Essential

* Vital

* Key

Other:

* Certain

* Special

* Individual

* Singular

The best synonym for "particular" will depend on the specific context of your sentence. For example, if you are talking about a particular type of flower, "specific" or "unique" might be good choices. However, if you are talking about someone who is very picky, "fussy" or "demanding" might be more appropriate.