Unforeseen means not expected and not planned for. Unforeseen circumstances, an unforeseen delay, unforeseen consequences.
Due to unforeseen circumstances is the standard formula for cancelling anything without explaining why. In law it matters, since a contract may excuse a party for an unforeseen event but not for one they should have seen.
1adjectiveunforeseenNot expected and not planned for.
“The builders ran into unforeseen problems when they found old pipes under the floor.”
unforeseen is a quality.
From un- + foreseen.
Etymology from Wiktionary, CC BY-SA