The Collaborative International Dictionary of English v.0.48:

Augmentative \Aug*ment"a*tive\, n. (Gram.)
   A word which expresses with augmented force the idea or the
   properties of the term from which it is derived; as, dullard,
   one very dull. Opposed to diminutive. --Gibbs.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Augmentative \Aug*ment"a*tive\, a. [Cf. F. augmentatif.]
   Having the quality or power of augmenting; expressing
   augmentation. -- Aug*ment"a*tive*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

augmentative
    adj 1: increasing or having the power to increase especially in
           size or amount or degree; "`up' is an augmentative word
           in `hurry up'"
    2: intensifying by augmentation and enhancement [syn:
       augmentative, enhancive]