Anchor showing unusual stamina, say -- finally (8)
I believe the answer is:
mainstay
'anchor' is the definition.
('mainstay' can be a synonym of 'anchor')
'unusual stamina say finally' is the wordplay.
'unusual' indicates an anagram.
'finally' says to take the final letters.
The last letter of 'say' is 'y'.
'stamina' anagrammed gives 'mainsta'.
'mainsta'+'y'='MAINSTAY'
'showing' is the link.
(Other definitions for mainstay that I've seen before include "Chief source of support" , "Piece of rigging" , "big support" , "chief supporter" , "Bulwark" .)