Quiver, like the elderly duke taking more rum? (6)
I believe the answer is:
dodder
'quiver like the elderly' is the definition.
(as in a doddery person)
'duke taking more rum?' is the wordplay.
'duke' becomes 'd'.
'taking' says to put letters next to each other.
'more rum?' becomes 'odder' (rum can mean odd).
'd'+'odder'='DODDER'
(Other definitions for dodder that I've seen before include "Walk unsteadily along the Dublin river?" , "Totter into the Dublin river" , "Progress unsteadily (due to age?)" , "Hesitate" , "move unsteadily" .)