wingspan n.

late 12c., wenge, "forelimb fitted for flight of a bird or bat," also the part of some insects resembling a wing in form or function, from Old Norse vængr "wing of a bird, aisle, etc." (cognate with Danish and Swedish vinge "wing"), of unknown origin, perhaps from a Proto-Germanic *we-ingjaz, suffixed form of PIE root *we- "blow" (source of Old English wawan "to blow." Replaced Old English feðra (plural) "wings" (see feather). The meaning "either of two divisions of a political party, army, etc." is first recorded c. 1400; theatrical sense is from 1790.

The slang sense of earn (one's) wings is 1940s, from the wing-shaped badges awarded to air cadets on graduation. To be under (someone's) wing "protected by (someone)" is recorded from early 13c. Phrase on a wing and a prayer is title of a 1943 song about landing a damaged aircraft.

"distance between two objects," from Old English span "distance between the thumb and little finger of an extended hand" (as a measure of length, roughly nine inches), probably related to Middle Dutch spannen "to join, fasten," from Proto-Germanic *spannan, from PIE root *(s)pen- "to draw, stretch, spin."

The Germanic word was borrowed into Medieval Latin as spannus, hence Italian spanna, Old French espan "hand's width, span as a unit of measure," French empan. As a measure of volume (early 14c.), "what can be held in two cupped hands." Meaning "length of time" first attested 1590s; that of "space between abutments of an arch, etc." is from 1725. Meaning "maximum lateral dimension of an aircraft" is first recorded 1909.