Catalan word existir comes from Latin de, Latin sistere, Latin sisto

Detailed word origin of existir

Dictionary entry	Language	Definition
de	Latin (lat)	(Late Latin) of persons. From, away from, down from, out of; in general to indicate the person or place from which any thing is taken, etc., with verbs of taking away, depriving, demanding, requesting, inquiring, buying; as capere, sumere, emere, quaerere, discere, trahere, etc., and their compounds.. From, away from, to indicate the place from which someone or something departs or [...]
sistere	Latin (lat)
sisto	Latin (lat)	(intransitive) I place myself; I stand.. (intransitive) I stand still; I halt; I stand firm.. (intransitive, legal) I appear in court.. (transitive) I cause to stand; I set; I place.. (transitive, legal) I cause to appear in court.
exsisto	Latin (lat)	(third-person) there is, there are. I am, exist.. I appear, arise, emerge.. I become.. I stand out (as), I stand out in regard to (+ dative).
existir	Catalan (cat)	To exist, to be.

Words with the same origin as existir