You see, all those Greek words, made up by people who were not Greeks at a time when creating "new" Greek words was fashionable, are more or less opaque for whomever does not have much familiarity with the so called Psi world. They are compound terms, sharing the first bit, "psych-" (which comes from Psyche, i.e. Soul.)
So, we have:
- Psychiatrist < Psychiatry < psyche + iatreia, ‘cure’.
- Psychologist < Psychology < psyche + logos, 'discourse, study'
- Psychotherapist < Psychotherapy < psyche + therapeia, 'nursing, cure'
- Psychoanalyst < Psychoanalysis < psyche + analysis, 'separation into components, close examination'
All this is very interesting, but did not answer the question. What's the difference?
A psychiatrist is a medical doctor. Psychiatrists deal with diseases of the mind. They regard your mental discomfort as a symptom of something pathological and they try to treat that. Many times they prescribe medication and then follow up your progress in a more or less regular but always medical way. They see you, they assess the severity of symptoms, they adjust any medication or any other treatment prescribed and arrange to see you again.
A psychologist is not a medical doctor. Psychologists engage with the scientific study of human or animal mental functions and behaviours. They do not deal with diseases (even though the so called Clinical Psychologists do study them) and they do not treat them. They share, of course, terminology with psychiatrists, but their main focus is studying rather than "curing" or "treating" an "illness".
Now what about Psychotherapy and Psychoanalysis. What are they?
Putting aside for a moment the differences between them, we can say that both Psychotherapy and Psychoanalysis are neither "scientific" in the way Psychology is, nor "medical" in the way Psychiatry is. Psychotherapists and Psychoanalysts do not deal with objective, measurable phenomena, in the way a servant of "hard sciences" would. More than the objective aspects of human suffering they are interested in its subjective ones: What is the difficulty you are facing? What was it in your own personal history that makes it so difficult to do such and such? Why do you find yourself unable to choose what is good for you? And so on, and so forth.
This is not to say that there is no objective aspect to human suffering, whatsoever. There might as well be. One might very well have an organic condition that is manifested as anxiety or stress or erratic reasoning. That's clearly a job for a medical doctor, possibly a psychiatrist. Of course, sometimes medical treatment leaves the subjective aspect of one's suffering untouched. If this is the case, then the psychotherapist / psychoanalyst will work in tandem with the psychiatrist.
More often than not, however, human beings suffer without any underlying medical condition. Being afraid that you will end up choosing the wrong type of person as a partner, lacking self confidence, or being frightened of open spaces –to bring some examples– are not illnesses as such, and they do not require medical attention. But they do require attention. This is what psychotherapists or psychoanalysts will offer.
To confuse things a bit, psychotherapists and psychoanalysts share some of the terminology of psychiatry. This is because that even though their approach is "not" scientific, not in the way of psychologists and medical doctors, anyway, psychotherapists and psychoanalysts do try to draw on their experience in the consulting room, and form some kind of theoretical understanding of what is happening.
So they will speak of schizoid personalities, paranoid psychoses, hysterical conversions, psychotic episodes and what have you. However, they will not do that in the consulting room. Terminologies and theories inform their practice but only indirectly. And when their clients ask them, "What's wrong with me, doctor, am I mad?", psychotherapists and psychoanalysts will avoid to give an answer, pointing out instead that they are not doctors, and that suffering is not a sign of madness.
And what about the difference between them, psychoanalysts and psychotherapists?
This is tricky. There are far too many schools of psychotherapy and psychoanalysis, that it is almost impossible to draw any clear dividing lines which would leave everyone satisfied. What I can say here is that psychotherapists tend to focus more on the "nursing" of one's suffering, often offering specific advice or suggesting coping strategies, while psychoanalysts refrain of doing so, focusing rather on the whys and hows of that suffering.
Ah, and before I forget: Psyche, in ancient Greek also meant "Butterfly", the connecting idea being that when you die, your soul flies away from your body like a butterfly.