Ἀνένδεκτόν [1 verse]( adj sg neut nom )"Impossible" is anendektos, which means "inadmissible", "impossible."-- The "impossible" here is a very rare word in written Greek, occurring only here and one other place.  It is made of a negative prefix with a root word that means "allowed" or "possible". This is more like "not allowed" than the "not capable of" word translated as "impossible" in Matthew 19:26.