The word "quiescence" comes from the Latin word quiescentia, meaning "rest" or  "quietness".  This noun quiescence comes from the Latin verb quiescere, meaning "to rest" or "to become quiet". Ultimately, this traces back to the Proto-Indo-European root *kweie-, which also means "to rest, be quiet".  Definition of Quiescence A state of rest or inactivity, Dormancy or stillness, and A temporary lull or pause.  According to the Oxford English Dictionary (OED), the earliest recorded use of the noun quiescence in English was in 1625.  The citation comes from the writings of the poet and clergyman John Donne.  

Quiescent is an adjective that means quiet, still, inactive, or in a state of rest or dormancy. It describes something that is not currently developing, functioning, or active.  According to the Oxford English Dictionary (OED), the adjective quiescent was first used in English in 1605.  The first recorded use was by philosopher and statesman Francis Bacon, in a passage that references Aristotle: "... as Aristotle endeavoureth to prove, that in all motion there is some point quiescent..." 

Examples of "quiescence" and "quiescent" used in a sentence: 
Environmental: "The forest experienced a period of quiescence during the winter, with no growth or movement." 
Geological: "Mount Fuji is an active volcano, but it is currently in a phase of quiescence, meaning it is not erupting." 
Biological: "To survive the cold, the insect entered a dormant, quiescent state to conserve energy." 
Social: "The community's political quiescence allowed for a long period of peace and stability". 
Professional: "The tech industry was in a quiescent period after a boom, with fewer new innovations emerging". 

Just the facts:

QUIESCENCE Definition & Meaning - Merriam-Webster

QUIESCENCE Synonyms: 74 Similar and Opposite Words | Merriam-Webster Thesaurus