remittent
Alternately increasing and decreasing in severity or intensity.
A remittent fever is when at certain periods the fever is more violent than at others, but the patient never intirely free from it.
Of or pertaining to remission of the severity of symptoms.
rare
[…] the long, long fever of life, which with him never knew a remittent moment, had robbed him of that which every man has a right to expect, some pleasure in the course of his existence.
Where it comes from
From Latin remittent-, present participle of remittō.
Adapted from the Wiktionary entry remittent (CC BY-SA 4.0).