No laughing matter is an idiom used to describe a serious or important situation that should not be taken lightly. There are many synonyms that can be used instead of this phrase to convey the same meaning. For example, one might say that something is a grave matter, a weighty issue, a serious concern, or a significant problem. Other synonyms for no laughing matter include a solemn affair, a sobering situation, a crucial matter, or a matter of great consequence. When using synonyms for no laughing matter, it is important to choose words that accurately convey the gravity of the situation and to use them appropriately to convey the desired message.