1. (organic chemistry) a specific grouping of elements that is characteristic of a class of compounds, and determines some properties and reactions of that class
   "The hydroxyl group is an important functional group in organic chemistry"
    
2. (ecology) a collection of organisms of specific morphological, physiological, behavioral, biochemical properties
   "Decomposers form a crucial functional group in ecosystems"

Derived forms: functional groups

Encyclopedia: Functional group