saliva, slobber
涎 centers on the liquid that flows from the mouth: saliva, especially when it drips or is produced in excess, like slobber.
涎 combines 氵 (water) with 延, which likely contributes the sound and the idea of something extending or flowing out, suggesting saliva flowing from the mouth.
Water 氵 beside 延 (extend) paints a picture of liquid extending from the mouth: saliva or slobber.
For セン, imagine a scene where saliva drips onto a hundred (百, ひゃく) sen coins: sen -> セン, and the drool extends over them.
drool
avid desire; craving; thirst; envy
bib; drool bib
object of avid desire; object of envy
avid desire; drooling over (something); watering at the mouth
drooling; hypersalivation; sialorrhea
very attractive thing; something to drool over
ambergris