Some types of letters — i.e., messages that you write on a piece of paper and send to someone — have their own name.
In fact, for example, we call 'note' a short letter to someone, 'rejection' a letter that tells you that you did not get a job or were not accepted by a school, 'response' a reply to any question or letter, and so on.
Even a letter sent regularly to members of an organization, containing news, has a name, 'newsletter', which is, as in the cases already mentioned, a single word.
That being said, my question is, is there a single word which one can use to refer to a 'love letter' — i.e., 'a letter telling someone how much you love them'?
Best Answer
Wiktionary gives billet-doux, which is technically a borrowed word, but is used in the English language in the same manner as any borrowed term, such as crime passionnel.
The only alternative I can think of is the conditional term "Valentine" which can mean "An expression of affection, especially romantic affection, usually in the form of greeting card, gift, or message given to a person the object of affection, especially on February 14th.". While it is conditional, it is the only single word term for a love letter that I could find.
Otherwise it appears that there is no single word term.
As a last note, I would like to point out that the noun "rejection" is not commonly used to refer to a rejection letter; if you have heard it used as such, it was probably being used as a colloquialism or in a context where its meaning was obvious. For example a situation in which a person holding a letter states "It's a rejection". Even in that context, its usage would be uncommon, people almost always say "rejection letter" in full.