| Rank | Word | Letters |
|---|---|---|
| 1. | Supercalifragilisticexpialidocious (1964) Wonderful, from song of this title in the film Mary Poppins. |
34 |
| 2. | Floccinaucinihilipilification (1741) The action of habit of estimating as worthless |
29 |
| 3. | Honorificabilitudinitatibus (1599) Honourableness |
27 |
| 4. | Antidisestablishmentarians (1900) Those opposed to the disestabilishment of the Church of England |
26 |
| 5. | Overintellectualization (1922) Excessive intellectualization |
23 |
| 6. | Incircumscriptibleness (1550) Incapable of being circumscribed |
22 |
| Omnirepresentativeness (1842) The quality of being representative of all forms or kinds |
22 | |
| Reinstitutionalization (1978) Institutionalize again |
22 | |
| 9. | Undercharacterization (1968) To depict or play with insufficient characterization or subtlety |
21 |
| 10. | Lithochromatographic (1843) Colour printing technique using stone |
20 |
* Source: Oxford English Dictionary
These are all non-medical terms or names of chemical compounds, which can be much longer in lengths.