Characteristic of eternalist oddly ignored (5)
I believe the answer is:
trait
'characteristic' is the definition.
(a trait is a quality or characteristic)
'eternalist oddly ignored' is the wordplay.
'oddly ignored' indicates alternate letters (letters in odd-numbered positions removed).
The alternate letters of 'eternalist' are 'TRAIT'.
'of' is the link.
(Other definitions for trait that I've seen before include "Feature of personality" , "Habit" , "Mannerism" , "Distinguishing feature" , "A characteristic of straitened kind" .)