Origin and history of substation

late 13c., stacioun, "a place one normally occupies," from Old French stacion, estacion "site, location; station of the Cross; stop, standstill," from Latin stationem (nominative statio) "a standing, standing firm; a post, job, position; military post; a watch, guard, sentinel; anchorage, port" (related to stare "to stand," from PIE root *sta- "to stand, make or be firm").

The meaning "fixed uniform distance in surveying" is from 1570s. The meaning "each of a number of holy places visited in succession by pilgrims" is from late 14c. in English; a similar notion is in Stations of the Cross (1550s). The meaning "regular stopping place" is recorded by 1797, in reference to coach routes; it was applied to stopping places on railroads by 1830.

The meaning "military post" in English is from c. 1600. The meaning "place where people are placed or sent for some special purpose, locality to which a functionary is appointed" (as in polling station) is by 1817, in police station "place where a police force is assembled when not on duty;" station house "police station" is attested from 1836.

The meaning "place for transmitting radio or television signals" is from 1912, in radio station; station break, a pause in broadcasting to give the local station a chance to identify itself, is attested from 1942.

The figurative or extended sense of "status, rank" (one's "place" in the scale of society) is from c. 1600.

word-forming element of Latin origin meaning "under, beneath; behind; from under; resulting from further division," from Latin preposition sub "under, below, beneath, at the foot of," also "close to, up to, towards;" of time, "within, during;" figuratively "subject to, in the power of;" also "a little, somewhat" (as in sub-horridus "somewhat rough"), from PIE *(s)up- (perhaps representing *ex-upo-), a variant form of the root *upo "under," also "up from under," which also yielded Greek hypo- and English up.

The Latin word also was used in Latin as a prefix and in various combinations. In Latin it was reduced to su- before -s- and assimilated to following -c-, -f-, -g-, -p-, and often -r- and -m-.

In Old French the prefix appears in the full Latin form only "in learned adoptions of old Latin compounds" [OED], and in popular use it was represented by sous-, sou-; as in French souvenir from Latin subvenire, souscrire (Old French souzescrire) from subscribere, etc.

The original meaning is now obscure in many words from Latin (suggest, suspect, subject, etc.). The prefix is active in Modern English; the indication generally being:

1. "under, beneath, at the bottom of;" in adverbs "down, low, lower;"

2. "inferior part, agent, division, or degree; inferior, having subordinate position" (subcontractor) also forming official titles (subaltern);

It also can indicate "division into parts or sections;" "next below, near, close to" (subantarctic); "smaller" (sub-giant); and it may be used generally as "somewhat, partial, incomplete" (subliterate).