More abstruse; more difficult to understand or more mysterious than something else.
From abstruse + -er comparative suffix. Following the pattern for one-syllable and some multi-syllable adjectives in English that add -er instead of using 'more.' The base word comes from Latin abstrusus.
Interestingly, 'abstruser' is technically correct but sounds awkward to modern ears—most English speakers today would say 'more abstruse' instead. This shows how English is slowly shifting away from -er comparatives for longer words.
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