An Etymological Dictionary of Astronomy and Astrophysics

1. To become smaller, shorter, tighter, as a metal when cooled.
   

2. To reduce to smaller size by or as if by squeezing or forcing together, e.g. contract a muscle.
   → contraction, → gravitational contraction, → Kelvin-Helmholtz contraction, → length contraction, → Lorentz contraction, → vena contracta.

Etymology (EN): From M.E., from O.F., from L. contractus, p.p. of contrahere “to draw together,” from → com- “together” + trahere “to draw.”

Etymology (PE): Terengidan, variant taranjidan [Dehxodâ] “to contract, become rough and hard, to be squeezed, compressed,” Borujerdi terengessa “cramped, tightly dressed,” Malâyeri terengidan “to be tightly dressed, cramped in a garment,” related to tarang “horse girth, a strap for fastening a load,” Proto-Iranian *trng- “to pull tight, squeeze, compress;” PIE base *strenk- “to pull tight, twist; tight, narrow” (cf. L. stringere “to bind or draw tight;” Gk. strangein “to twist;” Lith. stregti “to congeal;”
O.E. streccian “to stretch,” streng “string;” Ger. stramm,
Du. stram “stiff”).