caplet vs envelope

caplet

noun
  • A smooth-coated tablet (pill, as in medicine) shaped like a capsule, used as a tamper-resistant alternative to a capsule, or an easy-to-swallow alternative to regular tablets. 

  • A component of an interest rate cap, a derivative instrument that effectively prevents the interest payments on an otherwise variable-rate loan from exceeding an agreed level (the "cap"). Each "caplet", analysable as a call option, covers one interest accrual period (such as three months); the whole interest rate cap is made up of a series of consecutive caplets. 

envelope

noun
  • Something that envelops; a wrapping. 

  • An enclosing structure or cover, such as a membrane; a space between two membranes 

  • A curve that bounds another curve or set of curves, as the modulation envelope of an amplitude-modulated carrier wave in electronics. 

  • A mathematical curve, surface, or higher-dimensional object that is the tangent to a given family of lines, curves, surfaces, or higher-dimensional objects. 

  • A paper or cardboard wrapper used to enclose small, flat items, especially letters, for mailing. 

  • The nebulous covering of the head or nucleus of a comet; a coma. 

  • The set of limitations within which a technological system can perform safely and effectively. 

  • The shape of a sound, which may be controlled by a synthesizer or sampler. 

  • The information used for routing a message that is transmitted with the message but not part of its contents. 

  • An earthwork in the form of a single parapet or a small rampart, sometimes raised in the ditch and sometimes beyond it. 

  • A bag containing the lifting gas of a balloon or airship; fabric that encloses the gas-bags of an airship. 

How often have the words caplet and envelope occurred in a corpus of books? (source: Google Ngram Viewer )