What does "alter" mean?

Additional senses

1. 2.To geld. [Colloq.] Change is generic and the stronger term. It may express a loss of identity, or the substitution of one thing in place of another; alter commonly expresses a partial change, or a change in form or details without destroying identity.
2. 3.To become, in some respects, different; to vary; to change; as, the weather alters almost daily; rocks or minerals alter by exposure. "The law of the Medes and Persians, which altereth not." Dan. vi. 8.