expression, pre-noun adjectival
now gone; no longer existing; lost
A fixed literary expression used before a noun to indicate that something or someone no longer exists, often with a nostalgic or elegiac tone.
今は無き古都の面影をしのぶ。
I recall the vestiges of the now-lost ancient capital.
今はなき友を思って涙がこぼれた。
Tears fell as I thought of my friend who is no longer with us.
亡き is a classical attributive form of 亡い meaning 'dead' or 'deceased', used specifically for people. 今は無き is broader, referring to anything that no longer exists.
A fixed phrase combining 今 (now) + は (topic marker) + 無き (classical attributive form of 無い, 'not exist'). The use of the classical attributive 無き instead of modern 無い gives it a literary, nostalgic feel.