Crumbling bone found in tumulus? (8)
I believe the answer is:
moribund
'crumbling bone found in tumulus?' is the definition.
I can't tell whether this defines the answer.
'bone found in tumulus?' is the wordplay.
'bone' becomes 'rib' (rib is a type of bone).
'found in' indicates putting letters inside.
'tumulus?' becomes 'mound' (tumulus is a kind of mound).
'rib' placed inside 'mound' is 'MORIBUND'.
Can you help me to learn more?
(Other definitions for moribund that I've seen before include "Lifeless" , "In terminal decline" , "Stagnant - dying" , "In a dying state" , "lacking vitality" .)