ally (n.) Look up ally at Dictionary.com
late 14c., "relative, kinsman," from ally (v.); mid-15c. in the sense of "one united with another by treaty or league."
ally (v.) Look up ally at Dictionary.com
late 13c., "to join in marriage," from Old French alier "combine, unite," from a differentiated stem of aliier (from Latin alligare "bind to;" see alloy). Meaning "to form an alliance, join, associate" is late 14c. Related: allied; allying.