The Collaborative International Dictionary of English v.0.48:

gibberellic acid \gibberellic acid\ n. (Chem.),
   A plant growth hormone of the gibberellin series
   (C19H22O6), also called gibberellin A3. It was first
   isolated from the fungus Gibberella fujikuroi. It is used
   to promote the growth of seedlings. See also gibberellin.
   --MI11
   [PJC]

The Collaborative International Dictionary of English v.0.48:

gibberellin \gibberellin\ n. (Chem.),
   Any of a number plant growth hormones, the first of which was
   isolated in 1938 from the fungus Gibberella fujikuroi; more
   than 60 related gibberelins are known. The most important is
   gibberellin A3, also called gibberellic acid. They are
   used in agriculture for promoting plant growth.
   [WordNet 1.5 +PJC]