legal term, from Latin sistere "to cause to stand" (see assist).
Examples from the Web for sist
Cyst, sist, n. a bag in animal bodies containing morbid matter.
An' Sist' Humphreys, some way she git dem jailer-men be so kin' an' tender to 'im, lak I cayn't noways tell.
Discur′sion, desultory talk: act of reasoning; Discur′sist, a disputer.
But it ain't nare preachin' of Sist' Humphreys done give me a brokin an' a contrary hairt.
An' w'en my hairt be'n broke wid longin' an' mis'ry, Sist' Humphreys she come.