This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 唌 is uncertain. It visually combines 口 (mouth) with 延, but the original semantic and phonetic roles are unclear.
With 口 (mouth) beside 延 (prolong), imagine a prolonged sigh or lament, but remember the meaning is uncertain.
For セン, imagine a prolonged sigh that sounds like 'sen' escaping from the mouth: セン.