As others mentioned it was rape as "rapeseed". Unfortunate homophone of another word referring to non-consensual sex.
Middle English borrowed the word "rape" (for the seed) straight from Latin, rapum, rapa. The Latin word actually refers to turnips, but they're relatives and their flowers look really similar:
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Top is turnip (Latin rapa), bottom is rape. Latin inherited it from Proto-Indo-European [s]rā́p- "wild cabbage, turnip"; it's a really weird word, that ā shows it was borrowed into Late PIE from some pre-IE language.
Then the word referring to non-consensual sex was from Norman French "rap" instead. It's ultimately from Latin "rapere" (to seize, capture, rape), in turn inherited from Proto-Indo-European h₁rep- "to snatch".