na-adjective, noun which may take the genitive case particle 'no', noun
apathetic; unimpressed; unmoved
Describes a person or attitude that shows no emotional response or interest; often used for someone who is indifferent or hard to impress.
彼はどんな映画を見ても無感動だ。
He is unimpressed no matter what movie he watches.
無感動な態度で話を聞いていた。
He listened to the story with an apathetic attitude.
冷淡 means 'cold' or 'indifferent' in a more interpersonal, sometimes unfriendly way, whereas 無感動 is more about an internal lack of emotional reaction.
Compound of 無 (mu, 'without') and 感動 (kandō, 'deep emotion' or 'being moved'). The exact historical derivation is uncertain, but the word follows a common Sino-Japanese pattern for negation.