Latin, literally "by the way," from ob "to, toward" (see ob-) + iter "journey" (see ion). Klein's sources, however, say it is ob- with the suffix -iter in analogy of circiter "about" from circa. Also cf. obituary.
Examples from the Web for obiter
"It is an obiter dictum," somebody said to me, apparently thinking that Latin would persuade me.
Hence he forged his weapon—the obiter dictum—by whose broad strokes was hewn the highroad of a national destiny.John Marshall and the Constitution|Edward S. Corwin
The opinion of the Court was obiter dicens; but the Court expressed its opinion nevertheless.
But the judges of the circuit courts know better, and never have enforced that obiter dictum.