noun which may take the genitive case particle 'no', noun
immortal; everlasting; imperishable
Describes works, achievements, or fame that remain forever; formal and literary.
His work has been passed down as an immortal masterpiece.
This discovery left an everlasting mark on the history of science.
His achievements are immortal.
This piece is known as a timeless masterpiece.
不朽 (immortal, everlasting) and 普及 (widespread, diffusion) share the same reading ふきゅう but have completely unrelated meanings.
不朽 (immortal, everlasting) is a homophone of 不休 (without rest, tireless), so context is needed to tell them apart.
不朽 means eternal or immortal (as in lasting fame or work), while 不屈 means unyielding in spirit; the two share the 不 prefix and sound but differ completely in meaning.
From 不 (not) + 朽 (decay, rot). The kanji combination directly conveys 'not decaying', used metaphorically for lasting value.