One fled country to grasp second-tier maths (7)
I believe the answer is:
algebra
'maths' is the definition.
(algebra is a kind of maths)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for algebra that I've seen before include "part of curriculum" , "'Branch of mathematics, uses letters and symbols (7)'" , "Symbol-based mathematical calculation" , "Symbolic mathematics" , "Boolean speciality is raised" .)