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, and could not occur in Modern English, particularly not with wishful continuing in use. However, the sense of “longing” appears to be influenced by wishful, with wistful being an ambiguous poetic word.
- Full of yearning or longing.
- His eyes grew wistful as he recalled his university days.
- Sad and thoughtful.
- “wistful” in Douglas Harper, Online Etymology Dictionary, 2001–2017.