la juntura - joint, junction, juncture, place...
  la jungla - jungle
  jaque, jaque mate - check, checkmate (chess terms)
  el jarabe - syrup
  la jalea - jelly, gelatin dessert
  jaibón - pretentious, snobbish, stuck-up,...
  el jengibre - ginger
  la jeringuilla - syringe
  la jirafa - giraffe
  el karateka, la karateka - karate expert, someone who practices...
  Jehová, el Jehová - Jehovah or Yahweh (name of God often...
  la ictericia - jaundice
  el iceberg - iceberg
  integral - complete, comprehensive, total, made...
  el invierno - winter, rainy season (in the tropics)
  el interlineado - space between lines of text, leading
  interino - temporary, interim, stopgap, stand-in
  el IVA (impuesto sobre el valor añadido) - VAT (value-added tax)
  el islote - small island, usually rocky and...
  iracundo - angry, irate, irascible