singular plural - "An alternative mean" or "An alternative means"?

Despite ending with an s, means is (or can be) singular. An alternative means is no different from a means to an end, a means of communication, etc.

dictionary.com:

means (miːnz)

— n
1. ( functioning as singular or plural ) the medium, method, or instrument used to obtain a result or achieve an end: a means of communication

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