Template:A or an
From Heroes of Might and Magic: Olden Era Official Wiki
This template can be used on English-specific pages to check whether dynamic data should be preceded by "a" or "an". There are numerous exceptions to the usual consonant/vowel rule (such as "an honor", "a union") but those are cheerfully ignored. If an exception becomes necessary, feel free to add them.
This is {{A or an|Thistle}} thistle
This is a thistle
This is {{A or an|Enforcer}} Enforcer
This is an Enforcer
