I've been using Anki to learn (English) words for a while now (I got tired of looking up words I come across in books and then not 'learning' them from that). I've noticed a few things:

* A short definition is harder to remember than a long, involved one. It feels like the short one doesn't give enough mental 'hooks' for connecting to other concepts.

* A word that sounds onomatopoeia-c is usually easy to remember -- a 'cosh' is a bludgeon, and I have no trouble remembering that because it sounds kinda like one - one-syllable, harsh, blunt

* Words that don't seem to have definitions related to their spelling are hard to remember -- I had the hardest time remembering the meaning of the word "prevaricate" - 'to speak evasively, skirting the truth', because 'pre' makes no sense in it and 'vari' is not a root I've heard before, and neither has anything to do with lying

* Learning the etymologies of complicated words helps a lot, especially if it fixes the previous problem -- after learning the root 'aestus' means fire/boiling, but came to refer to the tide as the 'boiling of the ocean', I can't forget that estuaries are tidal zones of water

* Learning a story behind a word makes it hard to forget -- for instance I remember the word 'boffin' (Britishism for 'nerd') because I remember how it was used positively to refer to the war-effort researchers in Britain in WWII

* Using the word in a reasonable sounding sentence (not an idiomatic usage, 'the one way the word is ever used') helps a lot -- for instance, find a way to use the word "mores" that isn't in the phrase "social mores" and it's going to stick a lot better

* Words that come packaged with connotations are easier to remember -- for instance, the word 'lucre' means money or profit, but knowing that it usually means 'dirty money', specifically, as in money obtained via crime / sordid means, makes it way easier to associate it with a specific concept

* Talking to someone else about a word I learned makes it many times easier to remember -- for instance I gushed to a friend about the word 'psithurism', which is the 'sound of rustling leaves', and can't seem to forget it now

* Using a word in conversation / my own writing makes it far easier to remember than any amount of studying it via flash cards.

Basically it feels like the actual way to really learn a word is to associate a big mental structure around it in my mind - to understand subtleties in the definition; to associate it with its parts and roots and history; to have a social memory of sharing the word with someone else; to have to do the mental calculations to use it in my own speech or writing and to decide that it's the best word for what I wanted to say; etc.

This is consist with my experiences learning math and physics - I can learn a subject if I see it as a big picture, a narrative I can re-develop on the fly, or as a package of tools that are motivated by a particular kind of problem. I can remember an equation if I associate the parts of it with complicated mental frameworks or detailed arguments. But reading it off the page a bunch of times gets me almost nothing.

Cramming for a test usually means stuffing the raw text of the material into your brain, because you don't have time to build the whole concept lattice around it. I think that's why it doesn't work for retention.