trunnion
trunnion
UK[ˈtrʌnɪən]US[ˈtrʌnɪən]
n
either of a pair of cylindrical projections on opposite sides of a structure (such as a cannon or a telescope) that serve as a pivot for mounting it.
n
a supporting cylindrical projection on each side of a gun carriage, on which the gun pivots in elevation.
Etymology
the word "trunnion" entered english in the early 17th century from the french "trognon," meaning "core, stump, or trunk." the french term itself is of uncertain origin but is thought to be related to words for a tree trunk or a rounded, projecting part. the semantic shift from a general rounded stump to the specific technical meaning of a pivot pin on artillery is a classic example of a word being adopted and its meaning narrowed within a specialized field, in this case, military engineering. the logic of the word's evolution lies in the visual and functional analogy: just as a tree trunk is a central, supporting column, a trunnion is the sturdy, cylindrical projection that supports and allows the pivotal movement of a heavy cannon.
Analysis
the word is a simplex loanword from french. it does not contain separable, meaningful morphemes in its modern english spelling.
Examples
the cannon was mounted on its carriage, rotating smoothly on its heavy iron trunnions.
the engineer inspected the trunnion bearings for any signs of wear or misalignment.
the design incorporates large trunnions to support the weight of the rotating telescope assembly.