Regularly, one sees a wild elk in an English river (6)
I believe the answer is:
weekly
'regularly one' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I can't see?
'a wild elk in an english river' is the wordplay.
'a wild' indicates an anagram.
'in' indicates putting letters inside.
'an english river' becomes 'wey' (River Wey).
'elk' is an anagram of 'ekl'.
'ekl' put within 'wey' is 'WEEKLY'.
'sees' is the link.
Can you help me to learn more?
(Other definitions for weekly that I've seen before include "magazine" , "52 times a year" , "eg Every Tuesday" , "Periodical" , "Occurring every seven days" .)