1786, "decorative chest of drawers for holding clothes, handy articles, etc.," earlier (1680s) name of a type of fashionable ladies' large, high headdress mounted on a wire frame, from French commode, noun use of adjective meaning "convenient, suitable," from Latin commodus "proper, fit, appropriate, convenient, satisfactory," from com-, here perhaps an intensive prefix (see com-), + modus "measure, manner" (from PIE root *med- "take appropriate measures"). Meaning "chair housing a chamber pot," usually kept in a bedroom, is first attested 1851 from notion of "convenience."
I wash'd and patch'd, to make me look provoking,
Snares that they told me wou'd catch the men;
And on my head a huge commode sat cocking,
Which made me shew as Tall agen:
[from a song in "Wit and Mirth," 1719]