Russian imperial line that ruled from 1613 to 1917 (7)
I believe the answer is:
romanov
'russian imperial line that ruled from 1613 to 1917' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for romanov that I've seen before include "Russian house" , "Russian imperial family name" , "Family name of tsars" , "Russian dynasty before the Bolshevik Revolution" , "(Member of) Russian imperial dynasty" .)