World's Money Exchange, Inc. - Orders
... (Gold, Silver, Platinum bar and coins), PPM. Foreign Remitence. Purchase,
Purchase Remitence (Foreign Drafts and Foreign Wire Transfers), SREM. ...
www.wmeinc.com/orders/OrderMenu.asp - 15k - Cached - Similar pages

I don' t know your context, but here are the meanings:

remittance - 1. the sending of money, checks, etc., to a recipient at a distance 2. money or its equivalent sent from one place to another.

"remittence" (or "remittency") is quite another thing and means:
n. abatement for a time and at intervals
e.g. remittence/remittency of symptoms.

There is also a Croatian word "remitent" in finance and means "payee" in English (Vladimir Ivir, "Rjecnik privr. ili drus.-politickog nazivlja").

Hope this helps.

Best,
olyx

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Note added at 2003-03-10 21:49:25 (GMT)
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The above examples are from the 2001 edition of the \"Webster\' s Encyclopedic Unabridged Dictionary of the English Language\", Thunder Bay Press, San Diego, C.A.

re•mis•sion \ri-"mi-shen\ noun (13c)
1: the act or process of remitting
2: a state or period during which something is remitted
(C)1997, 1996 Zane Publishing, Inc. All rights reserved (Webster)

The usage of this term is less common in finance, thus it would appear a good choice if we are talking about the unsold copies returned to the publisher, though this specific meaning is not attributed to any of the terms (including this one)offered here, at least not in any of the dictionaries I was able to get hold of. Why not play it safe and call it "unsold copies"?