na-adjective
transient; fleeting; ephemeral
Literary or formal adjective describing something as short-lived and insubstantial, like a bubble on water. Often used in poetic or philosophical contexts.
人生は泡沫的なものだ。
Life is ephemeral.
泡沫的な恋に終
It ended as a fleeting romance.
一時的 means 'temporary' in a neutral, factual sense, without the poetic nuance of 泡沫的.
Compound of 泡沫 (ほうまつ, 'bubble, foam') + 的 (てき, adjectival suffix). The word 泡沫 itself is of Chinese origin (cf. Mandarin pàomò).