One place where the last word happens to be first! (5)
I believe the answer is:
ideal
'one place' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'the last word happens to be first' is the wordplay.
'the last' suggests the final letters (I've seen 'the last of' mean this).
'happens' becomes 'eal' (I am not sure about this - if you are sure you should believe this answer much more).
'to' means one lot of letters go next to another (I've seen this in other clues).
'be first' becomes 'i' (I in Roman numerals eg Elizabeth I).
The last letter of 'word' is 'd'.
'd'+'eal'='deal'
'deal' after 'i' is 'IDEAL'.
'where' acts as a link.
Can you help me to learn more?
(Other definitions for ideal that I've seen before include "highly desirable" , "just the job" , "without flaws" , "Just perfect, couldn't be better" , "Perfect for the purpose" .)