Definition: an ardent desire or longing; especially: a feeling of loss or grief for something lost
Most of us are familiar with the word desire, which, in addition to a number of other things, can mean “something desired.” And some of us are familiar with this word’s less-common cousin, desideratum, which means “something desired as essential” (the plural of this word is desiderata). Yet far too few of us are familiar with what is perhaps the least-known member of this particular family, the word desiderium. All of these words come from the Latin desiderare (meaning “to long for”), yet only desiderium carries the meaning of having feelings for something that we no longer have, and wish very much that we did.
I have studied almost every principal writer on the subject, but must except the general History of China, translated by Father Moyrac de Mailla in Twelve volumes 4to, which I just saw, but could not obtain, and I regret it daily with all the fulness of that desiderium which so dear a head as Father Moyrac de Mailla’s demands.
—Thomas James Mathias (translator), The Imperial Epistle from Kien Long, Emperor of China, to George the Third, King of Great Britain, 1796