"body of constituents," especially "a body of persons voting for an elective officer," 1806, from constituent + abstract noun suffix -cy.
Entries linking to constituency
constituent n.
1620s, "one who appoints or elects a representative," from Latin constituentem (nominative constituens), present participle of constituere "to cause to stand, set up, fix, place, establish, set in order; form something new; resolve," of persons, "to appoint to an office," from assimilated form of com-, here perhaps an intensive prefix (see com-), + statuere "to set" (from PIE root *sta- "to stand, make or be firm").
The notion is "to make up or compose" a body by appointing or electing a representative. Meaning "voter in an election to a public office" is from 1714. Meaning "that which constitutes as a necessary part, a formative element" is from 1756.
-cy
abstract noun suffix of quality or rank, from Latin -cia, -tia, from Greek -kia, -tia, from abstract ending -ia (see -ia) + stem ending -c- or -t-. The native correspondents are -ship, -hood.