1. [n]  one whose prevailing mental imagery takes the form of inner feelings of action
2. [adj]  (of spores or microorganisms) capable of movement

MOTILE is a 6 letter word that starts with M.

1. \Mo"tile\, a. [See {Motive}.]
   1. (Biol.) Having powers of self-motion, though unconscious;
      as, the motile spores of certain seaweeds.
   
   2. Producing motion; as, motile powers.
   
   

2. \Mo"tile\, a. [See {Motive}.]
   1. (Biol.) Exhibiting, or capable of, spontaneous movement;
      as, motile cilia, motile spores, etc.
   
   2. Producing motion; as, motile powers.
   
   

3. \Mo"tile\, n. (Psychol.)
   A person whose prevailing mental imagery takes the form of
   inner feelings of action, such as incipient pronunciation of
   words, muscular innervations, etc.