Legal Question in Real Estate Law in California

Re: Where did the term unlawful detainer come from?

This centuries-old term comes to us from the 'law French' of the middle ages (brought to England by William the Conqueror).

Originally Latin 'detinere' meant to 'keep back' 'withhold' or 'restrain.' In Old French it was 'detenir' and in Anglo-French it became 'detener.' 'Detainer' is a noun formation of the verb 'to detain,' much as 'container' is a noun formation from 'to contain.'

A detainer is not always unlawful. Originally, there was a writ of detainer, issued by a court. To distinguish, the modern real-property offense against rightful possession is called 'unlawful detainer' but I suppose it could be called 'unlawful possession' with about the same meaning (except confusion with criminal law concepts such as possession of controlled substances).

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Re: Where did the term unlawful detainer come from?

"Detain" means to keep possession of. "Unlawful" means not having the legal right to do so.