Guosa is a constructed interlanguage originally created by Alex Igbineweka in 1965. It was designed to be a combination of the indigenous languages of Nigeria and to serve as a lingua franca to West Africa.

Guosa draws the bulk of its vocabulary from Hausa, Yoruba, and Igbo, either taken directly or made from a combination of words from these languages. English also provides many of the more technical terms, either directly or through one of the aforementioned African languages. Additionally, several words were produced a priori via sound symbolism, e.g. meeh "sheep", yanmu-yanmu "mosquito", and wuam "eat".

The different parts of speech are often derived from specific languages. Most concrete nouns are derived from Hausa, while verbs and abstracts are derived from Igbo or Yoruba. Additionally, words from all three source languages are often fused to create a word that resembles all three. For example, the Guosa word méni "what" is derived from Hausa menini, Igbo gini, and Yoruba kini, all meaning "what".

The exact phonological values or amount of distinct phonemes in Guosa is unknown. The consonant system is closest to that of Standard Igbo, but with a hard distinction between nasal consonants and plosives that that language lacks, and even adds prenasalized stops. It also adds the /l r w j/ of Yoruba and Hausa, but lacks the glottalized consonants of the latter.

Though Guosa once had the seven vowel system similar to that of Yoruba, the vowels /ɛ/ and /ɔ/ have seemingly been merged into their closed counterparts, giving Guosa a five vowel system like Hausa. Vowels can be either long or short, but the functional load of vowel length appears to be light, however, as very few minimal pairs exist when tone is taken into account. There are nasal vowels written with an ⟨n⟩ following a vowel, though this does not always indicate a nasal vowel. The functional load of these is also light and the vast majority of nasal vowels are short. No two words differ in both the nasality of the vowels and vowel length.

It is unknown if there are diphthongs in Guosa; all vowels could be pronounced as separate syllables, or several vowels could form diphthongs. The phonology of Yoruba, however, suggests that Guosa vowels do not form diphthongs, as almost all the words with adjacent vowels come from Yoruba, in which all vowels are pronounced separately.

There are three basic tones in Guosa: high, mid, and low; there are also two contour tones: low-rising and high-falling. Mid is left unmarked and is seemingly the default tone, high is written with an acute ⟨◌́⟩, low with a grave ⟨◌̀⟩. On short vowels the low-rising is written with a caron ⟨◌̌⟩ and high-falling with a circumflex ⟨◌̂⟩. With long vowels, the contour tones are split across the two vowels. With long vowels, the contour tones are written as two separate diacritics.

Elision takes place when two of the same vowels would be adjacent, or with certain grammatical particles. For example, when the plural marker é is placed before a word beginning with a vowel: é ómóntàkélé → émóntàkélé "little children". This elision can be written with an apostrophe when the two vowels are the same: ji inang → ji'nang "twenty four". It can also be written as an apostrophe when the elision spans two words that are not particles: sòngí ìsóngà → sòngí 'sóngà "sing a song".