 | Alpine Convention |
 | Alternate Process Specifies that the step is an alternative to the normal process step. |
 | Alto clef When the C-clef is placed on the third line of the stave, it is called the alto clef. As with all C-clefs, this line indicates the position of middle C. |
 | Altostratus cloud Altostratus is a middle altitude cloud genus belonging to the stratiform physical category characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus … |
 | Alum An old alchemical sign for alum or alumen. |
 | Alum (alternate) A 17th century chemical sign for alum. |
