strongback

Short definition from Wiktionary

Noun

1. 1
   The fore-and-aft spar extending from stem to stern on a lifeboat and serving as a raised spreader for a boat cover. (FM 55-501)
2. 2
   A strong bar placed across a hatch opening to hold hatch boards or hatch covers. (FM 55-501)
3. 3
   A load-bearing post with a T-shaped cross-section, where the short T-tail prevents bowing of the long post.
4. 4
   A backing pole used to reinforce and stabilize vertically-oriented sculptures.
5. 5
   A vertical structure used to support and stabilize a rocket, often hosting fuel and power umbilical connections. Usually retracted immediately before launch.