ineffable (adj.) -- incapable of being expressed; indescribable or unutterable

intrepid (adj.) -- resolutely courageous; fearless

limpid (adj.) -- characterized by transparent clearness; pellucid

pellucid (adj.) -- admitting the passage of light; transparent or translucent: the pellucid glass pane of her train car's upper wall out of which Martha stared on the day of her arrival to Buxton

luculent (adj.) -- easily understood; clear or lucid

negligible (adj.) -- not significant or important enough to be worth considering; trifling

trifling (adj.) -- of slight worth or importance