admiror/admirari/admiratum - I wonder/marvel at.
This is a verb of the 1st conjugation. It is a deponent verb; it is active in meaning, but passive in its inflection. It is a transitive verb, so can take a direct object in the accusative case. It appears more common, though, for it to be used intransitively - simply "they wondered" - or for a preposition to follow it. Using a preposition instead of a direct object is a common tendency in Ecclesiastical Latin.
It is a compound of the preposition ad with the verb miror. Miror also means to wonder, and in its usage seems not to differ from admiror, though it is far less common.
According to Lewis and Short, in classical Latin admirari means "to be in a state of mind in which something pleases us by its extraordinary greatness, its sublimity, or perfection; while mirari signifies to be surprised at, to have the feeling of the new, singular, unusual."
The English word 'admire' etc. is related.