For a light flickering:
* Ffliceriad: This is the most direct translation, emphasizing the quick movement of light.
* Llosgi'n ansefydlog: This translates to "burning unsteadily" and captures the idea of a wavering flame.
For a flickering image or feeling:
* Fflachio: This translates to "flash" but can also be used for a quick, fleeting image.
* Cymysgu: This means "mix" and could be used to describe a sense of uncertainty or an image that seems to fade in and out.
* Diflannu: This translates to "disappear" and could be used for a feeling or image that seems to vanish quickly.
The best Welsh word to use will depend on the specific context and what aspect of "flicker" you want to emphasize.