MEANING: noun:
1. The long back part of a tailcoat that hangs down.
2. The success of another person or organization. Usually used in the idiom “to ride on someone’s coattails” meaning to achieve success by association with someone successful.

ETYMOLOGY: Often a popular leader of a political party helps attract votes for candidates of the same party for other positions as well. For example, a popular presidential candidate results in more victories for congressional races of the same party. In other words, these other candidates ride on the coattails of the president. This is known as the coattail effect. From Old French cote (coat) + Old English toegl (tail). Earliest documented use: 1600.

COSTTAIL - what you pay for a Malpractice Insurance policy for claims relating to events that that might have happened in the past...after you retire and the policy is no longer in force (the "tail")

COALTAIL - The lighter particles which pass over a sieve in the milling, crushing, or purifying of coal (see "tailings")

COATTAILI, Zoltan (16 December 1882 – 6 March 1967): Hungarian composer born of Italian parents; ethnomusicologist, pedagogue, linguist, and philosopher, inventer of a method of teaching music, especially for children. See here.