For example, suppose I want to refer to the specific definition of 'nut' as 'a perforated block usually of metal that has an internal screw thread and is used on a bolt or screw'.
This is the 3rd definition on the page http://www.merriam-webster.com/dictionary/nut, but Merriam-Webster only allows linking to the page, not a specific meaning.
Wiktionary allows linking to sections in a page, so we can link to Noun or Verb forms for example, but that's still too coarse for this scenario.
This a reboot of a question on english.stackexchange.com which was closed as being off-topic for that site. (And at 7 years old is long in the tooth, maybe there is an answer now that didn't exist then.)