In typography and handwriting, a superior letter is a lower-case letter placed above the baseline and made smaller than ordinary script. The style has traditionally been distinct from superscript. Formerly quite common in abbreviations, the original purpose was to make handwritten abbreviations clearly distinct from normal words. These could also be used to enable the important words on signs to be larger. In technical terms, the superior letter can also be called the superscripted minuscule letter. In modern usage, with word processors and text entry interfaces, superscript and superior letters are produced in the same way and look identical, and their distinction would refer to their usage and not to their form.
With the coming of printing, pieces of type were cast to enable them to appear in print. These are still commonly used in French, Italian, Portuguese and Spanish, though their appearance in English has diminished. Not every letter in the alphabet has a piece of type cast for it as a superior letter. In the book Thinking in Type, by Alex W. White, it is stated that there are only twelve superior letters used in French and Spanish: a, b, d, e, i, l, m, n, o, r, s, and t. In English, however, 'h' is also sometimes rendered as a superior letter, as in 6th.
In French, certain abbreviations are written with the first letter(s) of the word they represent, followed by the final letter(s) in superscript. The superscript in this case is sometimes optional. Most commonly, this appears in the abbreviations of personal titles: Mgr (or Mgr) stands for monseigneur ("Your Grace"), Mlle (or Mlle) for mademoiselle ("Miss"), Me for maître ("Mr"), etc. Other abbreviations containing superior letters are mdise for merchandise ("merchandise"), échce for échéance ("due date"), and Mo for métro ("subway").
When ordinal numbers are abbreviated, superscript letters are generally used:premier: 1er ("first")
vingtième siècle: XXe siècle ("twentieth century")
quatre centième: 400e ("four hundredth")
énième: Nième ("nth")
In Spanish, they are known as letras voladas ("flying letters", in Spain) or voladitas (literally, "little flying" letters). At present, these letters are usually not underlined, though underlining them is acceptable. It is ruled that a period must be added immediately before them, despite the fact that this norm is often ignored.
Superior letters are used to shorten various words in order to save space: f.o (folio, "page"); titles: D.a (doña, "Lady", "Ms."); personal compound given names: M.a Cristina (María Cristina) and regular administrative expressions: imp.to (impuesto, "tax").
For ordinal numbers, shortened forms use the ordinal indicators º and ª, rather than the superscript o and a, except in ordinal numbers ending in -er:primero: 1.º ("first")
segunda: 2.ª ("second")
tercer: 3.er ("third")
vigésimo quinto: 25.º ("twenty-fifth")
In English, superior letters are reserved for use with ordinal numerals, though this use is not mandatory and not always preferred: 1ˢᵗ, 2ⁿᵈ, 3ʳᵈ, etc.
Previously, in English-speaking countries, abbreviations of given names were used for recordkeeping. Today, their use is very uncommon, and they are generally only found in historical records. These abbreviations sometimes employed superior letters; for example, Alexr for Alexander, Nics for Nicholas.
Most typewriters for Spanish and other Romance languages had keys that could enter o and a directly, as a shorthand intended to be used primarily with ordinal numbers, such as 1.o for first.
In computing, early 8-bit character sets as code page 437 for the original IBM PC (circa 1981) also had these characters. In ISO-8859-1 Latin-1, and later in Unicode, they were assigned to and are known as U+00AA FEMININE ORDINAL INDICATOR (ª) and U+00BA MASCULINE ORDINAL INDICATOR (º). Here, "feminine" and "masculine" refers to grammatical gender. In Spanish, Portuguese, Galician and Italian, gender is usually distinguished by the suffixes -a and -o. These ordinal indicators are now distinct from the superior o and a characters. In the most of common available computer fonts today, ordinal indicators are not underlined.
One abbreviation using a superior letter, the numero sign, has been given its own character: №. Originally, this was just another use of a superior o, abbreviating numero, the word for "number" in several Romance languages. It often appears in English, for example in № 2 pencil, for "number-two pencil".
In Unicode, it is assigned to character U+2116 NUMERO SIGN (№) within the Letterlike Symbols block.
Both the code page 437 (position 252) and Unicode (U+207F SUPERSCRIPT LATIN SMALL LETTER N) have the character ⁿ to represent the n-th power of a number or variable in mathematics, for example 3ⁿ.
Several superior letters are used in phonetic transcription systems. The International Phonetic Alphabet uses the superscript n ⁿ for nasal release, the superscript w ʷ to indicate labialized or labio-velarized consonants, the superscript h for aspirated consonants, the superscript j ʲ for palatalized consonants, the superscript gamma for velarized consonants, the superscript turned h ᶣ for labio-palatalized consonants, the superscript reversed glottal stop for pharyngealized consonants, the superscript glottal stop is used for glottalized but pulmonic sonorants, such as [mˀ], [lˀ], [wˀ], [aˀ]. Other superscript letters are used as an alternative way to represent double articulated consonants, for example [tˢ] for [t͡s].