Fetus or Foetus: One Spelling Is a Mistake That Stuck
A fetus is an unborn offspring at a later stage of development. The British spelling with an o was based on a false Latin assumption.
A fetus is an unborn mammal after the main organs have formed. The British spelling *foetus* is historically wrong: the Latin word is *fetus*, with no o, and the extra letter was added by sixteenth-century writers who wrongly assumed a Greek connection. Medical journals worldwide now prefer *fetus*, and British style guides increasingly follow. In human development the term applies from about the ninth week; before that the word is *embryo*.
- An unborn offspring. *A healthy fetus.*
- Foetus — the British spelling. *The foetus.*
- Embryo — the earlier stage. *An embryo.*
- Fetal — of a fetus. *Fetal development.*
- Latin — *fetus*, offspring. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | fetus | One fetus. |
| Plural | fetuses | Two fetuses. |
| UK spelling | foetus | Foetus. |
| Adjective | fetal | Fetal heartbeat. |
| Latin | fetus | Offspring. |
- The scan showed a healthy fetus.Medicine.
- Before nine weeks it is an embryo.Stages.
- The o in foetus was a false correction.Spelling history.
False Latin corrections in English
- Foetus — an o added on a mistaken Greek assumption
- Debt and doubt — a b added to match Latin
- Island — an s added to match isle
- Scissors — a c added under Latin influence
- Anchor — an h added, though the Latin had none
Latin *fetus*, offspring or bringing forth, from a root meaning to produce. The spelling *foetus* arose in the 1500s by mistaken analogy.
Which spelling should I use?
Fetus is preferred in medical writing worldwide. Foetus remains common in general British English.
When does an embryo become a fetus?
In humans, at about the ninth week of pregnancy, once the main organ systems have formed.