Dramming is a term first introduced in the liquor business (hence Drambui, several hypothesize) specifically in whiskey distilleries as far back as the 15th century and dram might be derivative from drachma/δραχμή (Greek coin itself derived from δράττω, ie. grasp a handful) denoting amount of monetary value and thus specific volume. In some Scottish bars a 'dram' is taken to mean a large or double whisky and the fluid dram is one-eighth of a fluid ounce, hence "a small drink of liquor" (1713) [1] The term was also used as a an intransitive verb: 'To drink drams, to tipple' and as a transitive verb: 'to ply with drink'. Therefore dramming would be the practice of drinking drams of liquor. Free drams were passed around in distilleries to deter workers from pilfering.
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Dramming is defined as: "A technique for transferring a fragrance from a larger container to a smaller one. When stores have “dramming events” they are telling you that they have very large bottles of the fragrance, usually on display, that they will pour into a smaller one for you, usually in concert with special promotions". However please note the term "dram" in the decanting business (collectors who sell amounts of their own perfume collection) as well as the US medical field is a different still small amount: 1/16th of an ounce.
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Let it be said in passing that dramming bottles also circulate for popular cosmetics and skincare.
[1][2]Dictionary.comof Encyclopedia Britannica, 2008.
Thanks to perfumefanatic/POL for asking me the question in the first place.