The river in Hades takes no definite course (7)
I believe the answer is:
dithers
'takes no definite course' is the definition.
Although both the answer and definition are verbs in their -s form, I don't understand how they can define each other.
'the river in hades' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'in' indicates putting letters inside.
'hades' becomes 'dis' (I've seen this before).
'the'+'r'='ther'
'ther' put within 'dis' is 'DITHERS'.
Can you help me to learn more?
(Other definitions for dithers that I've seen before include "Hesitates indecisively" , "Flaps, wavers" .)