Dinosaur: “dī′no-sawr, n. a gigantic extinct reptile, which attained a length of eighty feet. [Formed from Gr. deinos, terrible, and sauros, lizard.]” From Chambers’s Twentieth Century Dictionary (part 1 of 4: A-D), 1911.
The term “Dinosauria” was submitted by zoologist and palentologist Richard Owen in a report to the British Association for the Advancement of Science in 1842 (not on this day in 1841, as reported by others). Dinosauria meant to Owen “fearfully great,” not “terrible lizard.”
An informal search for the word “dinosaur” (or variations) in dictionaries published after 1842 came up with nothing, until I found Chamber’s Twentieth Century Dictionary, published in 1911. Even then, the word does not appear to have been in common usage (according to various dictionaries) until after WWII.