non-arguable

adjective

1. susceptible to debate, challenge, or doubt; questionable: Whether this is the best plan of action or not is arguable.
2. susceptible to being supported by convincing or persuasive argument: Admirers agree that it is arguable he is the finest pianist of his generation.

adjective

1. capable of being disputed; doubtful
2. capable of being supported by argument; plausible

adj.1610s, from argue + -able.