Mortmain (noun) = the oppressive influence of the past on the present (pronounced ‘mawrt-meyn’)
e.g. To paraphrase writer Graham Greene, it’s clear that memory levies a mortmain on human beings: for our past experiences inform our present behaviour.
‘mortmain’ derives from the Latin, ‘mortua manus’, meaning ‘dead hand’ (a phrase that alludes to impersonal ownership – in fact, to an ownership so impersonal that it is as if a dead person is the owner).
It’s this concept, of the dead exercising posthumous control over their property by dictating how it must be used (long after they have died) that informs the meaning of ‘mortmain’, which refers to the ‘oppressive influence of the past’.
(Incidentally, in legal terminology, ‘mortmain’ is used to mean ‘the status of lands held inalienably, i.e. in a non-transferable way, by a corporation’.)