Wistful means gently sad about something lost or out of reach. A wistful smile, wistful about it, look wistful.
The gentleness is what makes it: wistfulness is longing without bitterness, which is why it suits memory and photographs of the past. It looks like wishful and is not related — it appears to come from an old word meaning silent or attentive. Note wistfully.
1adjectivewistfulGently sad about something lost or out of reach.
“She gave a wistful smile as she looked at old photos of her childhood home.”
synonyms: yearning, nostalgic
wistful is a quality of gentle longing.
WISTful → WISHful, and a little sad about it
Looking out of the window at something you wish you still had, half smiling about it, not really sad and not really over it.
hooks ontowish
Wistful is probably from whist, meaning silent or attentive, plus -ful. It is not related to wishful.
Built from
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.
Etymology from Wiktionary, CC BY-SA