This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 冿 is uncertain. It visually combines 冫 (ice) and 聿 (brush), but the component relationship is unclear.
With ice 冫 and brush 聿, imagine an ice brush that writes fleeting messages, but the meaning remains unclear.
For セン, think of a sen (千, thousand) ice brushes advancing: 千 -> セン, matching the kun reading すす.む (advance).