Inconstant (adjective)

1. Not staying the same; not remaining unchanged or consistent.
2. Not loyal or faithful; not steadfast.

Origin:

Late middle english: from old french, or from latin inconstans, from in- "not" + constans, constant- (see constant).

Examples:

1. The weather was inconstant, changing from sunny to rainy.
2. His inconstant moods made it hard for his friends to know what to expect.
3. Her inconstant attention made it hard for the teacher to keep her focused.
4. His inconstant behavior made it hard for her to trust him.
5. The inconstant nature of the stock market makes it hard to predict its movements.