There are various synonyms that can be used instead of "not very well." Some of these include poorly, inadequately, weakly, unsatisfactorily, insufficiently, insufficiently, indifferently, badly, substandardly, and unwell. These words can be used in different contexts, including health, performance, and overall status. For example, if someone is not feeling well, they may say that they are unwell or under the weather. Similarly, if something is not performed up to the standard, it may be described as being done poorly or substandardly. Regardless of the precise context, these synonyms provide a useful alternative to "not very well".