Yes, some words seem to be so hard to memorize - you may even wonder who on earth has created such a word or why they needed to create such a word.
It may help if you know the 'root' in a word, for example, it may help you memorize the word 'vocabulary' if you know the root 'vocabul' means 'word'. A lot of 'word roots' are Greek or Latin originated, which may seem alien or unfamiliar to you.
It may be so helpful if you can pronounce the word correctly. The most effective way, though, may be 'repeat' - the more you use the word, the more likely you'll memorize it.
However, you may need to try whatever works for you. For instance, 'ethic' and 'ethnic' are two different words and are so confusing, but there is an 'n' in 'ethnic' and 'n' may be related to 'nation':)
It may sound so funny, but it works for you. Anyway, you have managed to memorize the word.