receptor

[…] fewe that were there did spend the same daie abowte the searchinge out of sundrye that were receptors of ffelons, where we fownd a greate manye aswell in London, Westminster, Sowthwarke, as in all other places abowte the same.

In the target organ, the drug is recognised by ‘receptors’. These are large molecules, usually proteins, to which the drug binds tightly and with a high degree of specificity.