residency (n.)

mid-15c., "an inhabitant, one who dwells in a place permanently or for a considerable time," from resident (adj.). Meaning "medical graduate doing supervised specialized practice in a hospital as training" is attested by 1892, American English.

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.