Referring to TF:Prime toys as RID

[GoktimusPrime]

I always call gestalts combiners because I have no idea how I'd pronounce gestalts or what that even means. And gestalts are also referred to as combiners in official media so I don't see the problem there.

The problem is that during G1 gestalts never had an official encompassing name in English (except for the Scramble City gestalts who were called "Special Teams") - but Combiners were used in an official capacity to describe two Transformers that combined to form a single alt mode, i.e. the Micromaster Combiners.
http://www.youtube.com/watch?v=551a_2lLGuU

Because of this, around 1994 fans started using the word "gestalt" (which as Raptormesh said, means something that is greater than the sum of its parts) to describe gestalts like Devastator, Defensor, Bruticus, Superion, Menasor, Computron, Lio Kaiser et al. thus allowing the term "Combiner" to be used to describe combiners (like say Sledge and Hammer) without confusing them with gestalts.

It wasn't until as late as 2001 that the term "Combiners" was officially used to define gestalts for Robots In Disguise - and then again during Revenge of the Fallen when we had "Combiner Class" Devastator (but at the same time we also had ice-cream truck Skids and Mudflap who are more like the old G1 definition of a Combiner!). So anyway, now the term "Combiner" has been officially used to describe both Transformers whose single alt mode is an amalgam of two Transformers AND what fans commonly refer to as "gestalts."

'Gestalt' has been used officially a few times.

Yeah, "gestalt" was officially used in 2007 and 2009. However fans have been using it since 1994, so it was originally a fan-term. There have been several fan terms that have gained official currency, such as Bumper, Darkside, Generation 1 etc.

IIRC the term has its origins in..........psychology, I think? Something like that? (Vague memory seeing it used in uni)

Yup.