/
ɪˈtəːn(ə)l, 
iː-/
adj.
   - lasting or existing forever. 
▸informal tediously lengthy or persistent.
 - valid for all time; essentially unchanging:
 eternal truths.
 - 
(the Eternal)
 an everlasting or universal spirit, as represented by God.
 
Phrase
- the Eternal City
 the city of Rome.  - eternal triangle
 a relationship between three people involving sexual rivalry. 
Derivative
- eternality
  
/ɪˌtəːˈnalɪti, iː-/
 n.  - eternalize
 or eternalise v.  - eternally adv.
  - eternalness n.
 
Etymology
ME: via OFr. from late L. aeternalis, from L. aeternus, from aevum ‘age’.