Why is the ninth month called September?
1660s, "action of detaching," from French détachement (17c.), from détacher (see detach). Meaning "portion of a military force" is from 1670s; that of "aloofness from objects or circumstances" is from 1798.
detachment de·tach·ment (dĭ-tāch'mənt)
The act or process of disconnecting or detaching; separation.
The state of being separate or detached.
Indifference to or remoteness from the concerns of others; aloofness.
Absence of prejudice or bias; disinterest.