Definition
To fluctuate is to move up and down without settling — like a wave, which is exactly what the Latin root fluctus means. Prices fluctuate, temperatures fluctuate, moods fluctuate. The word implies repeated, often unpredictable change around some middle level, not a single rise or fall. If a value climbs steadily, it increases; if it swings back and forth, it fluctuates.
Examples
- Oil prices fluctuated wildly throughout the year, frustrating forecasters.
- Her energy levels fluctuate depending on how well she has slept.
- Support for the proposal has fluctuated since it was first announced.
Synonyms
vary · oscillate · waver · swing · shift
In TOEFL & IELTS
Essential for IELTS Writing Task 1: when a line graph zigzags, 'the figure fluctuated between X and Y' is the precise verb, and 'fluctuation(s)' the noun. TOEFL lectures use it for animal populations and climate data. Pair it with adverbs — 'fluctuate wildly/slightly/seasonally' — to describe how unstable the movement is.