This is the 279th most frequent Hungarian word.
életét
The Hungarian word "életét" means "his/her/its life" (accusative case).
Here, 'életét' is the accusative singular form of 'élet', implying the direct object of the verb 'megmentette' (saved).
Az orvos megmentette a beteg életét.
The doctor saved the patient's life.
In this sentence, 'életét' is again used as an object, showing the life that was sacrificed.
A hős az országért áldozta fel az életét.
The hero sacrificed his life for the country.
Here, 'életét' is part of a possessive structure, referring to 'the life' in relation to the person described.