Extremely important stations (7)
I believe the answer is:
termini
'stations' is the definition.
(terminus is a kind of station)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for termini that I've seen before include "Final parts" , "Rail stations mainly in city centres" , "Main railway stations" , "Ends, extremities" , "Starting points, limits" .)