Lay clues about a river (7)
I believe the answer is:
secular
'lay' is the definition.
(I know that lay can be written as secular)
'clues about a river' is the wordplay.
'about' indicates an anagram.
'river' becomes 'r' (abbreviation for river).
'clues' is an anagram of 'secul'.
'secul'+'a'+'r'='SECULAR'
(Other definitions for secular that I've seen before include "Not spiritual" , "Non-religious" , "Lay" , "associated with those who are 21 [LAYMEN]" , "Concerning the laity" .)