The word "moody" describes someone who frequently changes their emotional state or mood, often in an unpredictable way. A moody person might go from feeling happy one moment to feeling sad or irritable the next, which can make their mood seem unstable or shifting.
The word "moody" originates from the Middle English term "mode," which meant "mood, temper, or disposition," and can be traced back to Old English "mōd," meaning "mind, heart, spirit," or "courage." Its usage has evolved to encompass the idea of a variable or changeable emotional state.