Different, exclusive, particular, rare, uncommon, or extraordinary. They mean unique.
Distinct, one-of-a-kind, unparalleled, exclusive.
You can use the word "demanding" as a synonym for "challenging."
The word 'unique' is an adjective, a word used to describe a noun.An adjective can be used preceding the noun it describes.Example: My grandmother was a unique person for her time.An adjective can be a subject complement following a linking verb. A subject complement restates the subject of the sentence.Example: Your style is really unique. (style = unique)An adjective can be an object complement, a word following the direct object that restates it.Example: People considered Warhol's art unique. (art = unique)
Substitute or exchange can be used instead of replace.
Another word you can use instead of formality is "politeness" or "etiquette."
Reliable.
fustrating
coerced
make
Protest
I apologize.
ubiquitous
superb
CLOSE
brainstorming
its vital to use referncing
walkway,feetway,
Or, Nor,both