A horizontal sidewall window sprinkler comprising: a frame including a body having an inlet, an outlet with an internal passageway extending between the inlet and the outlet along a sprinkler axis, the frame including a pair of frame arms spaced about a first plane bisecting the sprinkler frame, the frame arms being diametrically opposed about the outlet so as to be aligned in a second plane that intersects and is perpendicular to the first plane at the sprinkler axis, the frame arms extending axially from the body and converging toward the sprinkler axis to define a frame boss axially spaced from the outlet; and a fluid deflector coupled to the frame boss at fixed distance from the outlet and oriented so as to be bisected and symmetrical with respect to the second plane and asymmetrical with respect to the first plane to define a first deflector portion and a second deflector portion different than the first deflector portion, the fluid deflector including: a pair of radially extending slots diametrically opposed about the frame boss and bisected by the first plane; the first portion of the fluid deflector includes a first peripheral edge having a first arc length portion extending from one of the pair of diametrically opposed slots to the other, the first peripheral edge being defined by a radius of curvature centered at the sprinkler axis and constant over the first arc length portion, the first peripheral edge defining a first constant radius over the first arc length portion; the second portion of the fluid deflector includes a second peripheral edge having a second arc length portion extending from one of the pair of diametrically opposed slots, the second peripheral edge having a third arc length portion spaced apart from the second arc length portion with a planar edge extending between the second and third arc length portions, the planar edge being centered about the second plane and parallel to the first plane, the planar edge being located at a distance from the first plane that is less than the first constant radius of curvature of the first peripheral edge. a frame including a body having an inlet, an outlet with an internal passageway extending between the inlet and the outlet along a sprinkler axis, the frame including a pair of frame arms spaced about a first plane bisecting the sprinkler frame, the frame arms being diametrically opposed about the outlet so as to be aligned in a second plane that intersects and is perpendicular to the first plane at the sprinkler axis, the frame arms extending axially from the body and converging toward the sprinkler axis to define a frame boss axially spaced from the outlet; and a fluid deflector coupled to the frame boss at fixed distance from the outlet and oriented so as to be bisected and symmetrical with respect to the second plane and asymmetrical with respect to the first plane to define a first deflector portion and a second deflector portion different than the first deflector portion, the fluid deflector including: a pair of radially extending slots diametrically opposed about the frame boss and bisected by the first plane; the first portion of the fluid deflector includes a first peripheral edge having a first arc length portion extending from one of the pair of diametrically opposed slots to the other, the first peripheral edge being defined by a radius of curvature centered at the sprinkler axis and constant over the first arc length portion, the first peripheral edge defining a first constant radius over the first arc length portion; the second portion of the fluid deflector includes a second peripheral edge having a second arc length portion extending from one of the pair of diametrically opposed slots, the second peripheral edge having a third arc length portion spaced apart from the second arc length portion with a planar edge extending between the second and third arc length portions, the planar edge being centered about the second plane and parallel to the first plane, the planar edge being located at a distance from the first plane that is less than the first constant radius of curvature of the first peripheral edge. a pair of radially extending slots diametrically opposed about the frame boss and bisected by the first plane; the first portion of the fluid deflector includes a first peripheral edge having a first arc length portion extending from one of the pair of diametrically opposed slots to the other, the first peripheral edge being defined by a radius of curvature centered at the sprinkler axis and constant over the first arc length portion, the first peripheral edge defining a first constant radius over the first arc length portion; the second portion of the fluid deflector includes a second peripheral edge having a second arc length portion extending from one of the pair of diametrically opposed slots, the second peripheral edge having a third arc length portion spaced apart from the second arc length portion with a planar edge extending between the second and third arc length portions, the planar edge being centered about the second plane and parallel to the first plane, the planar edge being located at a distance from the first plane that is less than the first constant radius of curvature of the first peripheral edge.