Speaker's set down mnemonic method (4)
I believe the answer is:
rote
'mnemonic method' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'speaker's set down' is the wordplay.
'speaker's' indicates a 'sounds like' (homophone) clue.
'set down' becomes 'wrote' (I've seen this in another clue).
'wrote' is a homophone of 'ROTE'.
Can you help me to learn more?
(Other definitions for rote that I've seen before include "Repetition of something to be learned" , "By . . . . - from memory without thought" , "Repetition from memory" , "Learn by ____ (repetition)" , "Habitual routine" .)