a tough nut to crack
Hard to solve
A tough nut to crack is a person or problem that's difficult to understand, persuade, or solve.
The image is of a hard-shelled nut resisting efforts to open it: The detective found the suspect a tough nut to crack.
Sometimes shortened to tough nut: She's a tough nut—doesn't give anything away.
Test of ability
- obstacleSomething blocking the way
- problemMatter requiring resolution
- hurdleBarrier to leap over
- struggleLabored effort against resistance
hardship · ordeal · barrier · puzzle · enigma · conundrum · riddle · mystery
Firmly refusing to yield
- intransigentRefusing to compromise
- unyieldingRefusing to give way
- headstrongStubbornly self-willed
- adamantStubbornly refusing to yield
tenacious · bullheaded · dogged · willful · inflexible · obdurate · resolute · unbending
Elaborately detailed, many parts
- complicatedDifficult to understand
- convolutedExcessively complex or twisted
- labyrinthineExtremely complex and winding
- knottyComplex and difficult
thorny · perplexing · cryptic · tangled · impenetrable · dense · multilayered · nuanced
Ill-tempered, stubborn person
- holdoutOne refusing to participate
- hard caseUnyielding or difficult individual
- sticklerDemands strict adherence
- skepticOne who doubts claims
cynic · gatekeeper · critic · contrarian · interrogator · negotiator · client · prospect
challenge
Test of ability
struggle · hardship · ordeal · barrier · puzzle · enigma · conundrum · riddle · mystery · dilemma
obstinate
Firmly refusing to yield
- intransigentRefusing to compromise
- unyieldingRefusing to give way
- headstrongStubbornly self-willed
adamant · tenacious · bullheaded · dogged · willful · inflexible · obdurate · resolute · unbending · uncompromising
intricate
Elaborately detailed, many parts
- complicatedDifficult to understand
- convolutedExcessively complex or twisted
- labyrinthineExtremely complex and winding
knotty · thorny · perplexing · cryptic · tangled · impenetrable · dense · multilayered · nuanced · sophisticated
curmudgeon
Ill-tempered, stubborn person
- holdoutOne refusing to participate
- hard caseUnyielding or difficult individual
- sticklerDemands strict adherence
skeptic · cynic · gatekeeper · critic · contrarian · interrogator · negotiator · client · prospect · examiner
a tough nut to crackchild's play
Something extremely easy
a walk in the park · easy as pie · a breeze · no-brainer · easy pickings
a tough nut to crackopen book
One easily understood
approachable · warm and fuzzy · easy-going · forthcoming · transparent
tough, tougher, toughest, toughly, toughness, toughen, toughened, toughening, nuttier