Merriam-Webster Collegiate Dictionary - formation

 noun  Date: 15th century  1. an act of giving form or shape to something or of taking form ; development  2. something that is formed new word ~s  3. the manner in which a thing is formed ; structure the peculiar ~ of the heart  4. a major kind of plant growth (as forest, grassland, or tundra) characteristic of a broad ecological region  5.  a. any igneous, sedimentary, or metamorphic rock represented as a unit  b. any sedimentary bed or consecutive series of beds sufficiently homogeneous or distinctive to be a unit  6. an arrangement of a body or group of persons or things in some prescribed manner or for a particular purpose flying in ~