How come octo means 8 but october is the 10th months not the 8th

hmmm . makes me think :)

SEPTember (seven), OCTOber (eight), NOVember (nine), and DECember (ten) were originally placed as their names implied. The Romans added two months in the middle of the year (July and August) later on, skewing the numbers...apparently nobody decided to fix the names.

October used to be the eight month,
...... but things got complicated.

because it used to be the 8'th month, but then July and August got added in after the Roman emperors, Julius and Augustus.

And sept means 7, dec means 10, etc.

It was the 8th month of the old Roman Calendar if I'm not mistaken.