\A*ton"ic\, a. [Cf. F. atonique. See {Atony}.]
1. (Med.) Characterized by atony, or want of vital energy;
   as, an atonic disease.
2. (Gram.) Unaccented; as, an atonic syllable.
3. Destitute of tone vocality; surd. --Rush.

\A*ton"ic\, n.
1. (Gram.) A word that has no accent.
2. An element of speech entirely destitute of vocality, or
   produced by the breath alone; a nonvocal or surd
   consonant; a breathing. --Rush.
3. (Med.) A remedy capable of allaying organic excitement or
   irritation. --Dunglison.