When we say something is "hardly the thing", we usually mean that it is not appropriate or suitable for a particular situation. There are many synonyms that could be used to convey the same message. For example, we could say that something is unsuitable, inappropriate, or incongruous. It could also be described as being out of place, improper, or unfitting. In some cases, we might say that something is unseemly, awkward, or unbecoming. Other possible synonyms include unsatisfactory, unacceptable, or untimely. Whatever word we choose, the message is clear: this thing is not quite right for the situation at hand.