Meaning

noun a small third seat in the back of an old-fashioned two-seater

noun a man's detachable insert (usually starched) to simulate the front of a shirt

adjective (British informal) faulty; - John le Carre

originUnknown. Perhaps a use of Dicky, hypocoristic form of Dick, perhaps playing on its resemblance to tricky, sticky, or other similar-sounding words. Alternatively, perhaps an alteration of dickens.

Etymology from Wiktionary, CC BY-SA 3.0