| 1. | the 12th letter of the Greek alphabet (M, μ). |
| 2. | the consonant sound represented by this letter. |
| 3. | micron (def. 1). |

mu (myōō, mōō) n. The 12th letter of the Greek alphabet. See Table at alphabet. [Greek, of Phoenician origin; see my2 in Semitic roots.] |
Mu abbr.
Mache unit
| MUS Musca (constellation) |