From Cornell University Dept. of Animal Science:

embryonic lethal genotype: Genotype whose expression results in the prenatal death of the individual possessing it.

lethal genotype: Genotype whose expression results in the death of the individual possessing it.

Note lethal alleles or genotypes just cause a premature death. That death does not need to occur during embryonic development or childhood. Huntington disease typically causes a slow and sad decline to death in middle age. You only need one copy of this allele to get the diease. Hence, its classified as a autosomal dominant disorder.