Buttonholer refers to a person who persistently and annoyingly engages someone in a conversation or request for something. However, there are several other synonyms for this word that could be used in different scenarios. For example, the word 'harasser' could be used to indicate someone who is persistently bothering or annoying another person. Another word that can be used synonymously with buttonholer is 'badger'. This term refers to someone who is pestering or bothering someone by continually asking questions or making requests. Other synonyms for buttonholer include 'nag', 'pest', 'interrupter', and 'troublemaker', and each of these words could be used in place of buttonholer in different scenarios.