commemorate
The definition for commemorate is "To mark by a ceremony." Used in a sentence: Each year, the Franklins commemorate their anniversary by visiting the site of their first date.
futile
The definition for futile is "Without purpose, completely ineffective." Used in a sentence: Arguing with Andrew is futile because he never changes his mind.
heed
The definition for heed is "To pay attention to." Used in a sentence: "Heed my advice," the fortuneteller warned Sebastian when he tried to ignore her prophecy.
opportune
The definition for opportune is "Suitable or convenient." Used in a sentence: Quan stepped onto the platform at the most opportune time, just as the train pulled in.
preclude
The definition for preclude is "To rule out in advance." Used in a sentence: "Having cake now will preclude dessert later," said Amber's mother.