How to add synonym with a forward shash? Error failed to build synonyms

How to add synonym with a forward shash? Error failed to build synonyms.

Your problem is probably due to tokenization. This works for me:

DELETE my_index

PUT my_index
{
  "settings": {
    "analysis": {
      "filter": {        
        "my_synonym_filter": {
          "type": "synonym", 
          "synonyms": [ 
            "ac/dc => synonym_1"
          ]
        }
      },
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "whitespace",
          "filter": [            
            "my_synonym_filter"
          ]
        }
      }
    }
  }
}

POST my_index/_analyze
{
  "analyzer" : "my_analyzer",    
  "text" : "ac/dc"  
}

produces:

{
    "tokens": [
        {
            "token": "synonym_1",
            "start_offset": 0,
            "end_offset": 5,
            "type": "SYNONYM",
            "position": 0
        }
    ]
}

Yep I tried

"ac/dc, acdc" - it give an error.

ac/dc also doesn't work.

You probably still use the "standard" tokenizer which will split the token on the slash. Also you didn't mention the error you are getting. The example I posted works for me, so in order to help here we'd need more information.