irreplaceable
adj.adj. describing something or someone so special or unique that they cannot be replaced if lost.
adj. impossible to replace if lost or damaged; unique in value or significance. Often used to describe people with unique skills or items of immense sentimental or historical value.
This old family photo is irreplaceable.
The museum lost several irreplaceable artifacts during the flood last winter.
While most equipment in the laboratory can be reordered, the decades of handwritten research notes are entirely irreplaceable and must be stored in a fireproof safe.
From ir- + replaceable.
Typically used as a predicative adjective after 'be' or 'seem', or as an attributive adjective before a noun.
an unreplaceable lossan irreplaceable lossWhile 'un-' is a common prefix for negation, 'irreplaceable' is the standard form for this specific word.