palauttaessaan
Palauttaessaan is a Finnish grammatical form. It is the third infinitive form of the verb 'palauttaa', which means "to return" or "to restore". Specifically, it is the adessive case of the third infinitive. This form is used to indicate an action happening *while* another action is being performed, or as a temporal clause meaning "when returning" or "upon returning".
For example, the sentence "Löysin avaimet palauttaessaan takin" translates to "I found the keys when returning
The third infinitive in Finnish has several forms depending on the grammatical case and possessive suffix.