caller — A caller is a person who is making a telephone call.
client — A client of a professional person or organization is a person or company that receives a service from them in return for payment.
companion — A companion is someone who you spend time with or who you are travelling with.
customer — You can use customer in expressions such as a cool customer or a tough customer to indicate what someone's behaviour or character is like.
inmate — a person who is confined in a prison, hospital, etc.
patron — (in Mexico and the southwestern U.S.) a boss; employer.
recipient — a person or thing that receives; receiver: the recipient of a prize.
tenant — a person or group that rents and occupies land, a house, an office, or the like, from another for a period of time; lessee.
vacationer — a period of suspension of work, study, or other activity, usually used for rest, recreation, or travel; recess or holiday: Schoolchildren are on vacation now.
visitor — a person who visits, as for reasons of friendship, business, duty, travel, or the like.
bedfellow — You refer to two things or people as bedfellows when they have become associated or related in some way.
boarder — A boarder is a pupil who lives at school during the term.
company — A company is a business organization that makes money by selling goods or services.
frequenter — happening or occurring at short intervals: to make frequent trips to Tokyo.
lodger — a person who lives in rented quarters in another's house; roomer.
mate — a tealike South American beverage made from the dried leaves of an evergreen tree.
partaker — to take or have a part or share along with others; participate (usually followed by in): He won't partake in the victory celebration.
renter — a person or organization that holds, or has the use of, property by payment of rent.
roomer — a person who lives in a rented room; lodger.
sharer — the full or proper portion or part allotted or belonging to or contributed or owed by an individual or group.
sojourner — a temporary stay: during his sojourn in Paris.
transient — not lasting, enduring, or permanent; transitory.