Knotty

Making great mental demands; hard to comprehend or solve or believe

Similar to

Difficult

Hard

Derivation

Knottiness

Examples

I faced the knotty problem of what to have for breakfast

Highly complex or intricate and occasionally devious

Similar to

Complex

Derivation

Knottiness

Examples

A knotty problem

Tangled in knots or snarls

Synonyms

Snarled

Snarly

Similar to

Tangled

Derivation

Knot

Used of old persons or old trees; covered with knobs or knots