Incomprehensible use of semicolons in dictionaries leads to a lot of confusion.
There is no explanation in English grammar regarding the use of commas and semicolons in dictionary entries.
This is in the field of knowledge of lexicography, which is a branch of linguistics that deals with the creation of dictionaries.
There is very little information on lexicography on the Internet and it is difficult to find a specialist in lexicography to ask him this question.
One way out is to look in the dictionary preface or dictionary conventions. But this only works for paper dictionaries. Online dictionaries usually do not contain any description of how to use them.
Does anyone have the paper version of the Oxford Dictionary of English or another similar paper dictionary? Could you look up what the semicolon means in the preface or the conventions of your dictionary and write here what you can find?
The online Oxford Dictionary of English uses commas and semicolons in its definitions, and it is not clear why it uses commas in some cases and semicolons in others.
For example:
Regular – 4. Used, done, or happening on a habitual basis; usual.
Also – In addition; too.
Good – 2.2 Healthy, strong, or well.
bad – 2.2 Unfavourable; adverse.
The same situation is in the explanatory dictionaries of the Russian language. Semicolons are used in a similar way. This suggests that there is some kind of lexicographic rule that dictionary compilers follow.
In the preface of one well-known paper Russian dictionary, it is said that after a semicolon goes shades of meaning. However, nowhere there is a definition of a shade of meaning.
I suppose that а shade of meaning is a meaning that is slightly different, but not so different that it is necessary to put it into a separate definition under a different number.
Another large Russian academic paper dictionary in the preface says synonyms follow the semicolon. A number of paper dictionaries say nothing at all about this, although semicolons are heavily used in their dictionary entries. Moreover, there are dictionaries where synonyms go separately and, at the same time, there are also words in their dictionary entries separated by semicolons.
This all is very confusing.
The problem comes when we want to precisely determine the meaning of a word.
If synonyms go after a semicolon, then we can not consider them as a part of a definition and ignore them. If after a semicolon there is a shade of meaning, then for complete understanding, we still need to take into account what comes after a semicolon.
From my observations of English and Russian dictionaries, I came to the following conclusion:
The main definition goes up to the semicolon. The semicolon is usually followed by something like synonyms. But they are not entirely synonymous. These words show in what other senses people use and understand a word to be defined. That is, they are like synonyms in one direction.
Let's look at the example from the Online Oxford Dictionary of English:
Regular
4. Used, done, or happening on a habitual basis; usual
The main definition is: "Used, done, or happening on a habitual basis". In addition, people can use this word, understanding it as "usual". However, it is the synonym in one direction. It does not work in the opposite direction.
"Usual" is not always "regular". So it is not a complete synonym and we cannot use "usual" interchangeably with "regular".