To get off or disembark from an airplane; to exit an aircraft after landing.
From 'dis-' (off, down) combined with 'emplane' (to board an airplane), which itself combines 'em-' with 'plane.' The opposite of boarding, following the pattern of disembark.
This word emerged in the early 20th century with commercial aviation—it's a perfect example of how English creates new words by applying productive prefixes to new technologies.
Complete word intelligence in one call. Free tier — 50 lookups/day.