fickle
The definition for fickle is "Lacking constancy, changeable." Used in a sentence: The fickle Senji had a new best friend every month.
gravity
The definition for gravity is "Importance, significance." Used in a sentence: Understanding the gravity of his error, Ken offered his humblest apology.
implement
The definition for implement is "To carry out or accomplish." Used in a sentence: All Randolph needed to implement his plan was a moonless night and a long rope.
meticulous
The definition for meticulous is "Extrememly careful regarding details." Used in a sentence: The meticulous detective found every shred of evidence at the crime scene.
periodic
The definition for periodic is "Occurring at regular intervals." Used in a sentence: The periodic innterruptions of the cuckoo clock prevented Li from concentrating.