oxymoron (n.)

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