Weak duke sides with king over eastern mine (8)
I believe the answer is:
decrepit
'weak' is the definition.
(I know that weak can be written as decrepit)
'duke sides with king over eastern mine' is the wordplay.
'sides' says to hollow out the word (remove centre letters) (only the letters on the sides are used).
'with' says to put letters next to each other.
'king' becomes 'CR' (short for Carolus Rex, King Charles in Latin).
'over eastern' becomes 'e' (I am not sure about the 'over' bit.).
'mine' becomes 'pit' (down the pit).
'duke' with its middle removed is 'de'.
'de'+'cr'+'e'+'pit'='DECREPIT'
Can you help me to learn more?
(Other definitions for decrepit that I've seen before include "Depicter may be weakened by old age" , "Worn-out" , "Elderly, infirm" , "Worn out; infirm" , "Cited rep for being old and dilapidated" .)