Withdraws books probing core elements of Einsteinian physics (4)
I believe the answer is:
ebbs
'withdraws' is the definition.
(I've seen this in another clue)
'books probing core elements of einsteinian physics' is the wordplay.
I cannot really understand how this works, but
'books' could be 'bb' (two abbreviations for book) and 'bb' is located in the answer.
'elements' could be 'es' (E is an example) and 'es' is located in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ebbs that I've seen before include "Goes out like tide" , "fades away" , "Wanes" , "flags" , "Declines gradually" .)