Use your flash cards differently.
1. Go through about 10 at time (adjust up or down as necessary for your abilities).
2. Do each one until you get it correct three times in a row or three out of five times. As you succeed, move that card to another pile for another session.
3. With ones you can't get under the criteria for #2, come up with some sort of memory aid (mnemonic device). Whatever you can remember, even if it doesn't make sense -- A rhyme, associating it with a person or object etc; visualizing it, etc.
4. Do more than just read the cards. Say them out loud. Sometimes write them.
5. Practice sometimes from French to English; sometimes English to French.
6. At the next session. Go through all ten cards again, the same way.
7. After getting a card correct three sessions in a row or three out of five, then move that card to another pile, for review a couple of sessions later.
8. When finally getting to the pile from #7, any you miss, put back in the works.
9. As cards leave active session pile (from doing #7), add new cards.
10. Also occasionally use words in actual sentences, especially ones you have problems remembering.
11. Sessions should be fairly short, ideally, but also frequent. Long-term memory is best achieved through brief practice periods done frequently, than through long periods done just a few times or less.
Long-term memory is also aided by using multiple inputs: speaking, listening, reading, writing, comparing, analyzing, etc. You can group similar words together. Opposites together. Related words in categories or pictures. etc.
Have fun and be creative. Memorizing is the easiest mental activity, if you do it in short bursts very frequently. It doesn't have to be stressful.
Some advice on some of your examples:
cacher - hide (cache exists in English, pronounced like "cash", but meanings a hidden supply of food, money, ammunition, treasures, etc. I'm sure you've heard it).
gagner - to win, earn (in the sense of GAIN. gagn- similar to gain.)
For the others, try the techniques above. Just practicing them frequently may be enough. If not, come up with a memory technique of your own. Even a silly one. example: If I were learning French now, I might associate voler with Voldemort from Harry Potter. And he could fly in a way.
fun fact: voler - also can mean to steal. vol de mort = can mean theft of death (Rowling was brilliant with her names). (It can also mean: flight of death; vol = flight or death.)
Malfoy, also from Harry Potter is also two French words: mal = evil (bad, pain, etc as a noun); foy (old French spelling. foi - in modern French) = faith. So Malfoy = evil faith.
Forgive my nerdiness. :)
taught French; three other foreign languages to an intermediate level (by choice); native English speaker. tutored study skills; got very good grades.