incarceration (n.) Look up incarceration at Dictionary.com
"fact of being imprisoned," 1530s, from Medieval Latin incarcerationem (nominative incarceratio), noun of action from past participle stem of incarcerare "to imprison," from in- "in" (from PIE root *en "in") + carcer "prison, an enclosed space," from Proto-Italic *kar-kr(o)-, of uncertain origin.
It seems best to connect carcer with other IE words for 'circle, round object', such as [Latin] curvus, [Greek] κιρκος 'ring', [Old Norse] hringr, although not all of these have a good IE etymology. The reduplication in Latin carcer could be iconic; thus, the original meaning would have been 'enclosure'. [de Vaan]
The word appears earlier in English in an obsolete medical sense of "retention of pus" (early 15c.).