Describes acting without careful thought, often with a negative connotation. Used as a na-adjective.
Don't say such reckless things.
He troubled those around him with his thoughtless actions.
Almost always used with a negative expression (e.g., 滅多に〜ない) to mean 'rarely' or 'seldom'. The adjective itself means 'ordinary', but the negative construction is the core usage.
He rarely gets angry.
An opportunity like this is rare.
Prefix used in a few set phrases like 滅多打ち (indiscriminate beating) or 滅多切り (hacking wildly). Not freely productive.
We were beaten indiscriminately by the enemy.
「滅多切り」 means cutting wildly and indiscriminately.
He rarely gets angry.
If you say something so rash, you'll regret it.
An opportunity like this is rare.