Extinct bird, one primarily in strange comeback (4)
I believe the answer is:
dodo
'extinct bird' is the definition.
(I've seen this before)
'one primarily in strange comeback' is the wordplay.
'primarily' says to take the initial letters.
'in' indicates putting letters inside.
'strange' becomes 'odd' (I've seen this before).
'comeback' says the letters should be written in reverse.
The first letter of 'one' is 'o'.
'o' inserted inside 'odd' is 'odod'.
'odod' back-to-front is 'DODO'.
(Other definitions for dodo that I've seen before include "bird long dead" , "Repetitive extinct animal" , "Proverbially dead bird" , "Mauritian bird no more" , "Square" .)