in memoriam
preposition
in me·mo·ri·am ˌin-mə-ˈmȯr-ē-əm 
: in memory of —used especially in epitaphs
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Since the days of the Roman empire, the words In memoriam, followed by a name, have been found on monuments and gravestones. They may also appear in the dedication of a book or poem; Alfred Tennyson's greatest poem is his immense In Memoriam, written over a period of 17 years to mourn the death of his dear friend Arthur Hallam.
Word History
Etymology
Latin
First Known Use
1850, in the meaning defined above