More abstruse and most abstruse are the preferred forms over abstruser and abstrusest. Do not confuse abstruse (hard to understand) with obtuse (failing to understand).

Abstruse

Look closely at the following Latin verbs, all of which are derived from the verb trudere ("to push, thrust"): extrudere, intrudere, obtrudere, protrudere. Remove the last two letters of each of these and you get an English descendant whose meaning involves pushing or thrusting. Another trudere offspring, abstrudere, meaning "to push away" or "to conceal," gave English abstrude, meaning "to thrust away," but that 17th-century borrowing has fallen out of use. An abstrudere descendant that has survived is abstruse, an adjective that recalls the meaning of its Latin parent abstrÅsus, meaning "concealed."

1590s, "remote from comprehension," from French abstrus (16c.) or directly from Latin abstrusus "hidden, concealed, secret," past participle of abstrudere "conceal, hide," literally "to thrust away," from assimilated form of ab "off, away from" (see ab-) + trudere "to thrust, push" (from PIE root *treud- "to press, push, squeeze;" see threat). Related: Abstrusely; abstruseness.

In expounding the principles of the differential calculus, he started, as it were, from the level of his pupils, and ascended with them by almost insensible gradations from elementary to abstruse conceptions.

His clearness of statement and power of imparting interest to the most abstruse topics were the conspicuous features of his teaching, and in his various capacities as a scientific lecturer, a physiologist, and a practical physician, he was ever surrounded with large and increasing classes of intelligent pupils, to whom his eminently suggestive mode of instruction was specially attractive.

The statements joined "a whole series of abstruse historical comparisons that are repeatedly used to justify the Russian invasion of Ukraine," government spokesman Steffen Hebestreit said in Berlin during Friday's press conference.

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