The word "abstruse" contains the root "trus", but the word means "difficult to understand." Explain how "abstruse" might have acquired its meaning?

When it comes to English language, there are some words which are not a real word but which are created by making use of different word. Such words are called as word parts. For example - Jealousish is not a word, but by adding 'ish' at the end of the word jealous it becomes a word part. Word parts are of three types - affixes, bases, and roots. Here we will talk about the word 'abstruse' which contains the root 'true.' Root gives the word a basic meaning. Abstruse have acquired its meaning from the Latin word 'trudere' which means to push away. Till late 17th century it was the word 'Abstrudere' which was being used. Later the word 'Abstruse' survived which means difficult to understand.