sentry — a soldier stationed at a place to stand guard and prevent the passage of unauthorized persons, watch for fires, etc., especially a sentinel stationed at a pass, gate, opening in a defense work, or the like.
Four-or-more syllable rhymes
complementary — Complementary things are different from each other but make a good combination.
elementary — Of or relating to the most rudimentary aspects of a subject.
supplementary — Also, supplemental. of the nature of or forming a supplement; additional.
