“Cissexism” (or cissexual assumption or cisnormativity) is the appeal to norms that enforce the gender binary and gender essentialism, resulting in the oppression of gender variant (non-binary) and trans identities.
“Heterosexism” is a system of attitudes, bias, and discrimination in favor of opposite-sex sexuality and relationships. It can include the presumption that other people are heterosexual or that opposite-sex attractions and relationships are the only norm and therefore superior.
“Cisheterosexism“ * is the system at the intersection of heterosexism and cissexism where attitudes, biases, and discrimination contribute to the oppression of those who do not conform to gender-normative, essentialist or binary behaviors, identities, presentations or relationships.
*I did not coin this term, but I have been unable to find an origin. If any reader knows the proper attribution for any of these words, please comment below.