If a unit suffers one or more wounds from a devourer it is required to take a morale check at the end of the phase, it suffers a -1 penalty to its leadership.
The condition for the morale check and the -1 penalty is only one wound from a Devourer. The mention of the Devourer is clarification that the one wound must come from that weapon. So it is say that any number of wounds from any number of Devourers will only ever cause one -1 penalty.
"Fetch me another plaything. This one seems to have broken." -Urien Rakarth
Space Marine- "This planet is ours, witch."
Eldar- "No ... This planet is theirs ..."