In which to write numbers? (6)
I believe the answer is:
pencil
'numbers?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'in which to write' is the wordplay.
'in which' becomes 'cil' (I can't explain this - if you can you should give a lot more credence to this answer).
'to' says to put letters next to each other (I've seen this in other clues).
'write' becomes 'pen' (synonyms).
'cil' after 'pen' is 'PENCIL'.
Can you help me to learn more?
(Other definitions for pencil that I've seen before include "Writing instrument" , "Drawing instrument" , "Wooden writer" , "Writing tool" , "A writing stick" .)