Dictionaries define 肉麻 as nauseating; sickening; disgusting. But I don't think those are accurate because those words are showing disproval while 肉麻 could show approval depending on how you use it. The word is being used when somebody says something overly sweet. E.g.
A: 我太喜欢你了！ 我愿意天天和你在一起！
This might be a question for the ELL site. But I don't know how to describe the word precisely in English, so I might just ask here. Any suggestions? Thanks!