The Collaborative International Dictionary of English v.0.48:

natural family \nat"u*ral fam"i*ly\, n. (Biol.)
   a group of living organisms classed as a family in a
   toxonomic classification.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Family \Fam"i*ly\, n.; pl. Families. [L. familia, fr. famulus
   servant; akin to Oscan famel servant, cf. faamat he dwells,
   Skr. dh[=a]man house, fr. dh[=a]to set, make, do: cf. F.
   famille. Cf. Do, v. t., Doom, Fact, Feat.]
   1. The collective body of persons who live in one house, and
      under one head or manager; a household, including parents,
      children, and servants, and, as the case may be, lodgers
      or boarders.
      [1913 Webster]

   2. The group comprising a husband and wife and their
      dependent children, constituting a fundamental unit in the
      organization of society.
      [1913 Webster]

            The welfare of the family underlies the welfare of
            society.                              --H. Spencer.
      [1913 Webster]

   3. Those who descend from one common progenitor; a tribe,
      clan, or race; kindred; house; as, the human family; the
      family of Abraham; the father of a family.
      [1913 Webster]

            Go ! and pretend your family is young. --Pope.
      [1913 Webster]

   4. Course of descent; genealogy; line of ancestors; lineage.
      [1913 Webster]

   5. Honorable descent; noble or respectable stock; as, a man
      of family.
      [1913 Webster]

   6. A group of kindred or closely related individuals; as, a
      family of languages; a family of States; the chlorine
      family.
      [1913 Webster]

   7. (Biol.) A group of organisms, either animal or vegetable,
      related by certain points of resemblance in structure or
      development, more comprehensive than a genus, because it
      is usually based on fewer or less pronounced points of
      likeness. In Zoology a family is less comprehesive than an
      order; in botany it is often considered the same thing as
      an order.
      [1913 Webster]

   Family circle. See under Circle.

   Family man.
      (a) A man who has a family; esp., one who has a wife and
          children living with him and dependent upon him.
      (b) A man of domestic habits. "The Jews are generally,
          when married, most exemplary family men." --Mayhew.

   Family of curves or Family of surfaces (Geom.), a group
      of curves or surfaces derived from a single equation.

   In a family way, like one belonging to the family. "Why
      don't we ask him and his ladies to come over in a family
      way, and dine with some other plain country gentlefolks?"
      --Thackeray.

   In the family way, pregnant. [Colloq. euphemism]
      [1913 Webster]

WordNet (r) 3.0 (2006):

family
    n 1: a social unit living together; "he moved his family to
         Virginia"; "It was a good Christian household"; "I waited
         until the whole house was asleep"; "the teacher asked how
         many people made up his home" [syn: family, household,
         house, home, menage]
    2: primary social group; parents and children; "he wanted to
       have a good job before starting a family" [syn: family,
       family unit]
    3: a collection of things sharing a common attribute; "there are
       two classes of detergents" [syn: class, category,
       family]
    4: people descended from a common ancestor; "his family has
       lived in Massachusetts since the Mayflower" [syn: family,
       family line, folk, kinfolk, kinsfolk, sept,
       phratry]
    5: a person having kinship with another or others; "he's kin";
       "he's family" [syn: kin, kinsperson, family]
    6: (biology) a taxonomic group containing one or more genera;
       "sharks belong to the fish family"
    7: a loose affiliation of gangsters in charge of organized
       criminal activities [syn: syndicate, crime syndicate,
       mob, family]
    8: an association of people who share common beliefs or
       activities; "the message was addressed not just to employees
       but to every member of the company family"; "the church
       welcomed new members into its fellowship" [syn: family,
       fellowship]