This is the 3709th most frequent Spanish word.
perpetua
"Perpetua" means "perpetual" or "everlasting."
Here, 'perpetua' is used as an adjective describing 'cadena', meaning life-long or never-ending.
El condenado recibió cadena perpetua por sus crímenes.
The convict received life imprisonment for his crimes.
In this sentence, 'perpetua' is a verb form meaning to make something last forever or to sustain perpetually.
El amor perpetua nuestra felicidad incluso en tiempos difíciles.
Love perpetuates our happiness even in difficult times.
This instance sees 'perpetua' as part of a descriptive phrase about a law's enduring qualities.