a snag	szkopuł
a hitch	drobna komplikacja
a setback	przeszkoda
a glitch	drobna usterka
stumbling block	sth that prevents action of agreement, przeszkoda, zawada
pitfall	unexpected difficulty, pułapka , często plural
obstacle	anything that stops progress, either literally or metaphorically
impdiment	sth that prevents free action, progress of movement, wada, kalectwo, przeszkoda
dilemma	situation where a difficult choice has to be made between two, sometimes unpleasent alternatives
ordeal	severe experience, which is very difficult, painful or tiring, gehenna
adversity	niedola, tarapaty, przeciwność losu, trudności życiowe (more formal)
hardship	cierpienia, trudności (more formal)
affliction	niedola, nieszczęście, dolegliwość (more formal)
tribulation	udręka (more formal)
abstruse	difficult to understand - theory,argument,philosopher
arduous	difficult, titing, needing much effort - climb, task, journey
complex	difficult to understand as it has many parts - issue, problem, theory, process
convoluted	unreasonably tiring and difficult - journey, work, match, expedition - zawiły, zagmatwany
gruelling	extremely tiring and difficult - journey, work, match, expedition - wyczerpujący
obstructive	causing deliberate difficulties - person, measure - blokujący, stwarzający problemy
insufferable	difficult to bear as it is annoying or uncomfortable - behaviour, heat, boredom, pain
stiff	difficult to beat - opposition, competition - nieustępliwy, zacięty
tough	difficult to deal with or do - time, job, climate, decision
traumatic	shocking and upsetting - experience, past, childhood
wayward	changeable, selfish and/or hard to control - behaviour, child, person - krnąbrny, kapryśny
what a pain! / what a drag!	what a nuisance! (colloquial) x2
what's eating him? / what's got into him? / what's bugging him? / what's (up) with him?	what's the matter with him? (colloquial) x4
the hassle of doing sth	situation causing trouble or difficulty (colloquial) - kłopot, zawracanie głowy
to hassle sb for sth	to pester (gnębić, męczyć) sb, ask again and again for sth (colloquial) - zawracać głowę
to slog(your guts out), to grind(zakuwać), to graft(harować), to flog yourself to death	to work hard (colloquial) x4
in a fix, in a spot, in a hole, up against it, up to one's neck	in a difficult situation (colloquial) x5
sticky, tricky	difficult (colloquial) x2
to be off the hook, in the clear, out of the wood(s)	to be freed from a difficult sitation (colloquial) x3