word-forming element meaning "below, beneath," from Latin infra (adverb and preposition) "below, underneath, on the under side, beneath," also "later than; smaller than; inferior to," related to infernus "low, below," from PIE *ndher "under" (source also of Sanskrit adnah "below," Old English under "under, among;" see under). Modern popular use of it dates from the 1920s, as an opposite to super-, often in science fiction. "This use of infra- is scarcely a Latin one" [OED].
mid-15c., "action or process of building or construction;" 1610s, "that which is constructed, a building or edifice;" from Latin structura "a fitting together, adjustment; a building, mode of building;" figuratively, "arrangement, order," from structus, past participle of struere "to pile, place together, heap up; build, assemble, arrange, make by joining together," related to strues "heap," from PIE *streu-, extended form of root *stere- "to spread."
<a href="https://www.etymonline.com/word/infrastructure">Etymology of infrastructure by etymonline</a>
Harper, D. (n.d.). Etymology of infrastructure. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/infrastructure