Sorry if this has already been covered. On the objective knowledge and Defense it uses the word "destroyed". While this objective is undamaged, you may return friendly units DESTROYED during an engagement to their owner's hand instead of discardng them. Question: What does destroy mean? I can not find a definition in the rule book. If i sacrific a unit during an engagement can I return that unit to my hand?

My understanding is that destroy means something leaves play because it has damage >= capacity (per rules pg 21), or leaves play via an effect that uses the term destroy.

Rules for sacrifice say "choose and discard a card in play" - using the term discard here implies that sacrifice isn't a subset of destroy.