adj. phantom, phantomlike,  illusory
adv. in an illusory manner
n. phantom; illusion
v. to make or become illusory

Fiik lo sah!
Mirror deceive phantom!
(Phantom Form Shout)

Qethsegol vahrukiv sod do Siglif fin Vonun wo aam lot Keizaal ni ol kendov ko vu nuz ol sah ko suvulaan.
[(This) stone commemorates (the) deeds of Siglif the Unseen, who served great Skyrim not as (a) warrior in dawn, but as (a) phantom in twilight.]
(Unused Word Wall for Sah, Phantom Form)

Word of Power; false or unreal, typically ghostly or supernatural.