As far back as John Cowell's Interpreter (1607), an early law dictionary, there are separated senses in dictionary entries.

However, Johnson's Dictionary is more ambitious in this regard than its predecessors and in the Plan of a Dictionary of the English Language (1747) Johnson outlined his aim to organise each entry according to the following scheme:

In explaining the general and popular language, it seems necessary to sort the several senses of each word, and to exhibit first its natural and primitive signification, as To arrive, to reach the shore in a voyage. He arrived at a safe harbour.
 

Then to give its consequential meaning, to arrive, to reach any place whether by land or sea; as, he arrived at his country seat.
 

Then its metaphorical sense, to obtain anything desired; as, he arrived at a peerage.
 

Then to mention any observation that arises from the comparison of one meaning with another; as, it may be remarked of the word arrive, that in consequence of its original and metaphorical sense, it cannot be properly applied but to words signifying something desirable; thus, we say a man arrived at happiness, but cannot say without a mixture of irony, he arrived at misery.

This plan can be seen operating in a good many entries in Johnson's Dictionary, such as the following entry under the verb 'to eclipse':