In his travels, he wrote notes (5)
I believe the answer is:
ravel
'he wrote notes' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'in his travels' is the wordplay.
'in' indicates the answer is hidden within the clue.
'RAVEL' is hidden within 'his travels'.
Can you help me to learn more?
(Other definitions for ravel that I've seen before include "Tangle or become tangled" , "Make more complicated - French composer, d. 1937" , "He scored" , "Musician" , "Bolero's composer" .)