Omissio

Omissio is a Latin noun meaning omission or the act of omitting, derived from the verb omittere, to send away or let slip. In contemporary usage, the term appears in legal, philosophical, and rhetorical contexts to denote the act or result of excluding something that should be included or considered.

In law, omissio refers to failure to act when a duty to act exists. While many crimes require an affirmative act, liability may arise from omissions where a legal or fiduciary duty to intervene or disclose is present—for example, a parent’s duty to care for a child, a professional’s obligation to report, or statutes mandating intervention.

In tort and civil law, omissions can give rise to liability through negligence or breach of duty when failure to act proximately causes harm.

In logic and rhetoric, the fallacy of omission describes presenting an argument while suppressing relevant evidence or considerations, potentially misleading an audience. In ethics and bystander studies, omissions are evaluated to determine moral responsibility for not acting in dangerous situations.

Originating in Latin, omissio remains a general term across languages to denote non-inclusion, with specialized uses in law, rhetoric, philosophy, and linguistics.