This is the 4701st most frequent French word.
plongeant
"Plongeant" means "dipping" or "sloping downward."
Here, 'plongeant' is used as an adjective describing the sun in its action of setting or diving over the horizon.
Le plongeant soleil teignait le ciel en rouge.
The diving sun painted the sky red.
In this case, 'plongeant' refers to the neckline of a dress, describing its deep and descending style.
Elle portait une robe avec un décolleté plongeant.
She wore a dress with a plunging neckline.
Here, 'plongeant' is metaphorically describing the intensity and focus of the child's gaze, as if diving deep into thought or inquiry.