I am a native English speaker.
There are some words in English that we don't see or read or use very often.
It is not easy to remember the definitions of words from the dictionaries.
If we don't read those words very often, it is easy to forget the word's meaning or definition.
I always suggest that people look at the synonyms (words that mean the same thing or are very similar).
Here is a simple example:
The new word "humongous".
The easiest synonym to remember is "immense", and immense means "huge".
So, if you remember that humongous = huge, then you will understand and remember the word humongous.
Here is another example:
The new word (not used very often): "extraneous"
If we search for the word in a thesaurus (list of synonyms) [
http://www.thesaurus.com/], we will see the synonyms "extra / unnecessary".
So, extraneous = unnecessary, e.g. He provided a lot of extraneous (unnecessary/extra) information.
There is one more techniques I would recommend, however, it does not work for all the English words.
In the word "extraneous" you see the smaller word "extra".
In the word "dangerous" you see the word "danger".
In the word "remember" you see a small part of the word "memory".
So, seeing a small part of a word in a bigger word may help us to remember the meaning of the larger word.
These are my recommendations for remembering new words.