What is the difference between respect and aspect as nouns ?

Hi. What do you mean? These words have different meanings.

Could you write a sentence in which you are not sure which word to use?

Peter has a terrible temper. In this respect, he is the opposite of his sweet-natured brother.

Peter's temper is one aspect of his personality that I really do not like.

Oxford says:
respect
3[C] a particular aspect or detail of sth:
In this respect we are very fortunate. Ç There was one respect, however, in which they differed.

aspect
[C] a particular part or feature of a situation, an idea, a problem, etc.; a way in which it may be considered:
The book aims to cover all aspects of city life. Ç the most important aspect

You will find "respect" used like this: in every respect, in this repsect, in respect to ... You will often find it paired with "in."

I repeat the invitation to try to create sentences using these words to see which one seems to make sense.

With regard to those two definitions from Oxford, think of respect as way; think of aspect as way of looking at something or way of considering something.

In this [respect / way] we are very fortunate. There was one [respect / way], however, in which they differed.
The book aims to cover all [aspects of / ways of looking at / way of considering] cit