wistful
adj.adj. feeling or showing a quiet sadness because you are thinking about something you cannot have or a time that is gone. It is a gentle feeling of longing.
adj. characterised by a quiet, pensive sadness or longing for something unattainable or a past time. Often used to describe a person's expression or a nostalgic atmosphere.
She looked at the old photo with a wistful smile.
The old man spent his evenings walking by the lake, looking at the water with a wistful expression as he remembered his youth.
The novel's wistful tone captures the bittersweet nature of growing up, where the protagonist must leave behind the safety of childhood for the uncertain world of adulthood.
Presumably from whistful, from whist (“silent”) + -ful, based on older wistly. It is implausible that it derives from wishful, the required sound change being wishful → wisful → wistful, which could not occur in Modern English, particularly not with wishful continuing in use. However, the sense of “longing” appears to be influenced by wishful, making wistful an ambiguous poetic word.