Is it ensure, insure, or assure?
also shakedown, 1730, "impromptu bed made upon loose straw," from verbal phrase; see shake (v.) + down (adv.). Meaning "forced contribution" (1902) is from the verbal phrase in a slang sense "blackmail, extort" (1872). Meaning "a thorough search" is from 1914; perhaps from the notion of measuring corn. The oldest use of the verbal phrase shake down is "cause to totter and fall" (c.1400).
[final sense fr shakedown cruise; all senses fr the notion of a vigorous shaking of a person or place to reveal something hidden, a flaw, etc]