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COMPLEX, COMPLICATED, INTRICATE, INVOLVED, KNOTTY mean having confusingly interrelated parts.

COMPLEX suggests the unavoidable result of a necessary combining and does not imply a fault or failure.

e.g. a complex recipe

COMPLICATED applies to what offers great difficulty in understanding, solving, or explaining.

e.g. complicated legal procedures

INTRICATE suggests such interlacing of parts as to make it nearly impossible to follow or grasp them separately.

e.g. an intricate web of deceit

INVOLVED implies extreme complication and often disorder.

e.g. a rambling, involved explanation

KNOTTY suggests complication and entanglement that make solution or understanding improbable.

e.g. knotty ethical questions

very complicated or detailed:

〈模様･形などが〉込み入った, 入り組んだ, 複雑な; 〈話･構造などが〉難解な

e.g. an intricate network of canals.

late Middle English: from Latin intricat- ‘entangled’, from the verb intricare, from in- ‘into’ + tricae ‘tricks, perplexities’.