The words ‘kink’ and ‘fetish’ are often used synonymously. They are however quite distinct. To give you the Cliff Notes – most kinks aren’t fetishes, but fetishes are kinks.
When I sat down to this, I found a few conflicting definitions. So, in the interests of clarity, I had a dive into some clinical psychology.
It turns out Dr. Richard Sprott, a developmental psychologist, has written a number of rather helpful research papers. I had a bit of a rummage around those and came up with the following definitions:
‘Kink’ is an umbrella term used to describe a wide range of ‘non-normative erotic or positive emotion-arousing interests and behaviours’.
That is to say, it’s a broad term which is used to describe anything which makes you feel good, but is outside what is considered the mainstream.
This includes (but is certainly not limited to): eroticisation of sensations such as pain, power exchange, erotic role play, and yes, fetishes. But I’ll get to that in a moment.
What is considered the mainstream is, of course, incredibly subjective.
For example, I would describe the use of vibrators and sex toys as a normal and mainstream part of sex. But I have a vanilla friend or two who discuss sex toys in hushed tones as an exciting, yet distant, fantasy.
‘Kink’ has been used to describe our community for over 90 years. The first recorded use of the acronym ‘BDSM’ crops up in 1991, in the hatchling days of the Internet.
According to Sprott, the term was originally coined by researchers, and then adopted by the kink community.
So, in fact, the ‘kink’ umbrella is so wide that it can cover any BDSM practice.
A fetish is an ‘enduring fascination and arousal with specific sensory stimuli, including specific body parts or inanimate objects’, which aren’t considered sexual. 
That is to say, a ‘fetish’ describes a fixation on an object or body part with something which isn’t considered sexy.
Feet and / or shoes are a good example. They aren’t conventionally something which elicits a sexual response, yet plenty of people fixate on and get turned on by them.
But I thought a fetish was something someone needed to get turned on?
Well, so did I. And so do a lot of people.
In fact, a lot of assorted online sources define a fetish as something that is essential for the fetishist to achieve arousal or orgasm. Nooky Box goes even suggests that there is a spectrum which goes ‘vanilla – kink – fetish’.
Despite its popularity, I have found very little to support this idea.
Dr. Sprott doesn’t include it in his definition, and for good reason – a 2017 study on object fetishism found that most fetishist can (and do) enjoy sexual activities without their fetish object.
So, in my opinion, defining it as a matter of intensity makes very little sense. Both within the context of research conducted in this area, and our ‘instinctual’ feel for what a might call a fetish without thinking.
So, what’s the difference?
A ‘kink’ can describe pretty much any aspect of BDSM – it’s a giant umbrella. A fetish is a fixation on a non-sexy object or body part, which falls under that umbrella.
All fetishes are kinks, but most kinks aren’t fetishes.
 Richard A. Sprott, ‘A Queer Boundary’, (Sexualities Vol 24 Issue 5-6)