Study can ultimately define calcified tissue (7)
I believe the answer is:
dentine
'calcified tissue' is the definition.
(tissue forming teeth)
'study can ultimately define' is the wordplay.
'study' becomes 'den' (term for a study or office).
'can' becomes 'tin' (both are metal containers).
'ultimately' says to take the final letters.
The final letter of 'define' is 'e'.
'den'+'tin'+'e'='DENTINE'
(Other definitions for dentine that I've seen before include "Tooth material" , "Substance of which teeth are mainly composed" , "which forms tooth" , "Material in teeth" , "Tin need (anag.)" .)