Is there any difference between the words 'impressionable' and 'suggestible'? Are they neutral or slightly disapproving? There are so many words in English with a similar meaning, for example: 'susceptible', 'gullible', 'credulous', 'naive'... (all of these seem to be unfavorable, am I right?), and I was wondering if some of these are interchangeable.
It seems as though you have already looked up these words, so I will not bother providing the definitions again. Here are my impressions from personal experience:
“Gullible” and “credulous” are similar to each other, but the former is far more common. Most of the time it is used to say that someone is easily swindled or fooled by someone attempting to mislead them. This is probably the most insulting one on your list, and it’s not even that bad. “Credulous” just means that someone doesn’t question what they hear, which could make them easily fooled. It’s closer to “impressionable” or “naïve” in that way, but, again, not very commonly used.
From Cambridge Dictionaries Online:
"impressionable - describes someone, usually a young person, who is very easily influenced by the people around them and by what they are told, and who sometimes copies other people's behaviour."
"suggestible - describes someone who is easily influenced by other people's opinions."
So impressionable is associated with youth and mimic ing behaviour.
Suggestible is associated with vulnerability to other's words (written or verbal).
They are very similar.