-ule

"small case, natural or artificial," 1650s, from French capsule "a membranous sac" (16c.), from Latin capsula "small box or chest," diminutive of capsa "box, case, chest" (see case (n.2)). The medicinal sense is by 1875; its shortened form cap is attested from 1942. The sense in space capsule is recorded by 1954, perhaps from the earlier sense of "shell of a metallic cartridge" (1864). As an adjective from 1938. Related: Capsular.

1580s, "allotted measure," a sense now obsolete, from French module (1540s) or directly from Latin modulus "small measure," diminutive of modus "measure, manner" (from PIE root *med- "take appropriate measures").

Sense of "a standard measure to regulate proportions" is from 1620s. Meaning "interchangeable part" is recorded by 1955, via the notion of "length chosen as the basis for the dimensions of parts of a building, etc." (1936); that of "separate section of a spacecraft" is from 1961.