Frail stranger in empty doorway (7)
I believe the answer is:
doddery
'frail' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I don't see?
'stranger in empty doorway' is the wordplay.
'stranger' becomes 'odder' (more odd).
'in' indicates putting letters inside.
'empty' says to hollow out the word (remove centre letters).
'doorway' with its middle removed is 'dy'.
'odder' going into 'dy' is 'DODDERY'.
Can you help me to learn more?
(Other definitions for doddery that I've seen before include "Faltering" , "Shaky" , "Unsteady in movement" , "Old and feeble" , "Slow and unsteady" .)