paradox (n.)
- absurdity
- ambiguity
- ambivalence
- antinomy
- asymmetry
- contradiction
- crux
- dilemma
- disproportion
- enigma
- equivocation
- heresy
- heterodoxy
- heterogeneity
- hopelessness
- impossibility
- impossible
- impossibleness
- incoherence
- incompatibility
- inconceivability
- incongruity
- inconsistency
- irony
- knot
- mystery
- node
- nonconformity
- oxymoron
- perplexity
- poser
- problem
- puzzle
- quandary
- self-contradiction
- teaser
- unorthodoxy