customer

n. client, buyer; person one must deal with (Slang)

A customer is someone who makes use of or receives the products or services of an individual or organization. The word historically derives from "custom," meaning "habit"; a customer was someone who frequented a particular shop, who made it a habit to purchase goods there, and with whom the shopkeeper had to maintain a relationship to keep his or her "custom," meaning expected purchases in the future.
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Noun
1. someone who pays for goods or services
(synonym) client
(hypernym) consumer
(hyponym) buyer, purchaser, emptor, vendee
(member-holonym) business relation

(n.)
One who regularly or repeatedly makes purchases of a trader; a purchaser; a buyer.
  

(n.)
One who collect customs; a toll gatherer.
  

(n.)
A person with whom a business house has dealings; as, the customers of a bank.
  

(n.)
A peculiar person; -- in an indefinite sense; as, a queer customer; an ugly customer.
  

(n.)
A lewd woman.
  

generally any person or organisation who buys a product or service; not necessarily the end consumer (see consumer).