Shed much light in speech — it’s a skill (5)
I believe the answer is:
flair
This might be a double definition.
'shed much light in speech' is the first definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'it's a skill' is the second definition.
(I've seen this before)
Can you help me to learn more?
(Other definitions for flair that I've seen before include "Natural ability/talent" , "?lan, dash" , "Natural talent and aptitude" , "Elan; panache" , "Natural talent or panache" .)