Concedes there are about a thousand approaches (6)
I believe the answer is:
admits
'concedes there' is the definition.
'admits' can be an answer for 'concedes' (I've seen this in another clue). I am not sure about the 'there' bit.
'about a thousand approaches' is the wordplay.
'about' is an insertion indicator.
'a thousand' becomes 'M' (Roman numeral for a thousand).
'approaches' becomes 'adits' (I've seen this in another clue).
'm' placed inside 'adits' is 'ADMITS'.
'are' is the link.
Can you help me to learn more?
(Other definitions for admits that I've seen before include "grants us access" , "Owns up or lets in" , "Takes in" , "Concedes" , "Confesses or allows to enter" .)