also main-line, "inject (drugs) intravenously," 1934, from main line in American English slang sense "principal vein into which drugs can be injected" (1933).
It forms all or part of: defile (n.) "narrow passage;" enfilade; filament; file (v.1) "place (papers) in consecutive order for future reference;" filigree; filipendulous; fillet; profile.
It is the hypothetical source of/evidence for its existence is provided by: Avestan jya- "bowstring;" Latin filum "a thread, string;" Armenian jil "sinew, string, line;" Lithuanian gysla "vein, sinew;" Old Church Slavonic zila "vein."
1670s, in botany, "rootlet, part of the embryo of a plant which develops into the primary root," from Latin radicula, diminutive of radix "root" (from PIE root *wrād- "branch, root"). Anatomical sense of "branch of a nerve, vein, etc. resembling a root" is by 1830.
"blood-letting," c. 1400, flebotomye, fleobotomie, from Old French flebotomie (13c., Modern French phlébotomie) and directly from Medieval Latin phlebotomia, from Greek phlebotomia "blood-letting," from phlebotomos "opening veins," from phleps (genitive phlebos) "a vein" (a word of uncertain origin) + tomē "a cutting" (from PIE root *tem- "to cut").
"pertaining to the abdomen, ventral," 1550s, from medical Latin abdominalis, from abdomen (genitive abdominis); see abdomen. As a noun, "abdominal muscle," by 1961 (earlier "abdominal vein," 1928); earlier as a fish of the order including carp, salmon, and herring (1835), so called for their ventral fins. Related: Abdominally. English in 17c. had abdominous "big-bellied."