Exanistēmi (ἐξανίστημι) means to raise up or stand up — a strengthened form of anistēmi (G450, to rise), itself from ex (out of). In Mark and Luke it appears in the Sadducees' resurrection challenge (raising up offspring for a dead brother); in Acts 15:5 certain Pharisees "rose up" to insist on circumcision.
The Sadducees' question in Mark 12:19-23 uses exanistēmi for the Mosaic levirate duty — a brother raising up offspring for a dead brother. Their hypothetical (seven brothers, one wife) was designed to make resurrection seem absurd. Jesus' answer (Mark 12:24-27) reframes resurrection entirely: not resuscitated earthly life but transformed existence where marriage categories no longer apply. The same verb used for levirate raising is implicitly used for resurrection-raising — two meanings of "raising up" that Jesus distinguishes sharply.
Exanistēmi is the compound of anistēmi (the primary resurrection verb, G450) with the intensifying ex. The levirate use highlights the OT's this-worldly approach to "raising up" — legacy, name, offspring. Jesus' resurrection is different in kind: not raising up a name within the existing order but raising up persons into a transformed order. The Sadducees' category error was applying earthly logic to eschatological reality.