The Aramaic word דמסתפינא came up in a sefer of mine,would anyone know what it means ?
It literally means "that I am afraid." "לולא דמסתפינא"--"were it not that I am afraid" is a common rabbinic phrase typically signaling a novel interpretation which the author is not confident enough in to overturn precedent with.
The root is "ספי," meaning "fear." The suffix "נא" with the prefix "דמ" means "that I am." "ת" is because the construction is hitpa'el, and comes after the "ס" to make the word slide off the tongue easier.
See here, under the entry for "ספא, ספי."
EDITED in light of comments below.