The words "monosyllabic" and "disyllabic" seem to describe words with one or two sounds. I'm looking for a similar word, but that instead describes a word constructed from only one or two letters (e.g. "I" or "it").
As noted in previous comments, uniliteral ("consisting of a single letter") and biliteral ("composed of two letters") appear in various dictionaries and as noted refer to single-letter and two-letter constructions. However, the etymology of literal (as at etymonline) somewhat restricts the scope of literal, making it less applicable to ideograms:
literal (adj.) late 14c., "taking words in their natural meaning" (originally in reference to Scripture and opposed to mystical or allegorical), from O.Fr. literal and directly from L.L. literalis/litteralis "of or belonging to letters or writing," from L. litera/littera "letter, alphabetic sign; literature, books" ... Meaning "of or pertaining to alphabetic letters" is from late 15c.
The meaning of previously-suggested monoglyphic is "having only one siphonoglyph, the sulcus, as certain polyps: contrasted with diglyphic", where a siphonoglyph is a "ciliated groove at one or both ends of the mouth of sea anemones and some corals"; that is, the word does not treat of single-character words. Grapheme, also mentioned before, has forms monographemic, bigraphemic, and digraphemic that are used apparently for speaking of one- or two-character Chinese/Japanese/Korean words. For example, Sproat et al, 1996 say:
Put another way, written Chinese simply lacks orthographic words. In Chinese text, individual characters of the script, to which we shall refer by their traditional name of hanzi, are written one after another with no intervening spaces ... Partly as a result of this, the notion "word" has never played a role in Chinese philological tradition, and the idea that Chinese lacks anything analogous to words in European languages has been prevalent among Western sinologists [but] twentieth-century linguistic work on Chinese has revealed the incorrectness of this traditional view. All notions of word, with the exception of the orthographic word, are as relevant in Chinese as they are in English, and just as is the case in other languages, a word in Chinese may correspond to one or more symbols in the orthography: K. ren2 'person' is a fairly uncontroversial case of a monographemic word, and ~] zhongl-guo2 (middle country) 'China' a fairly uncontroversial case of a digraphemic word.
The terms monographemic, bigraphemic, and digraphemic serve for alphabetic single-letter and two-letter words as well. Per wikipedia:
A grapheme is the smallest semantically distinguishing unit in a written language, analogous to the phonemes of spoken languages. A grapheme may or may not carry meaning by itself, and may or may not correspond to a single phoneme. Graphemes include alphabetic letters, typographic ligatures, Chinese characters, numerical digits, punctuation marks, and other individual symbols of any of the world's writing systems.
The words are uniliteral and biliteral. I don't imagine there is any sensible alternative to either.
The words monographemic and digraphemic are sometimes used.
Why not just say "one-letter and two-letter words"?
Both uniliteral and biliteral are rarely-used complicated terms. It's difficult to find words which are very specific. Either the word is very uncommon or no word simply exists. In situations like this, it's better to combine the simpler words in a phrase with hyphens.
If you're looking for a word that has the same meaning as a phrase with two or more words, in most cases you can just hyphenate the words in the phrase. It gives your writing a modern feel and is more easy-to-understand at times.
Suppose, you want a single word to describe a person who isn't the type of person to joke or have any nonsense. Yes, there are words like stern, serious, solemn etc. However, do they address the exact subject you have in mind? A person who doesn't like jokes or nonsense isn't necessarily stern (which brings to mind the picture of a strict schoolteacher). Nor does he have to be a serious and solemn person (someone who speaks less and is only concerned with serious subjects like politics and environment). The person in question may just be practical. He can still be free (not stern) and outgoing (not serious and solemn).
You can't ever be satisfied with any word, if you go on like this. No word is perfect. Even synonyms aren't the same — each and every word has different connotations attached to it.
Hyphens come to the rescue! Why not say no-nonsense? It conveys the exact same meaning you want to convey. (No-nonsense is already a standard word. This was just meant to be an example.)
