Prefix · quantity · equal
Means "equal" or "same": isotope, isosceles, isometric, isobar, isotherm, isomer.
Written by Bryan López, English teacher · Updated
Iso- comes from the Greek isos, which means "equal" or "identical". It appears almost always in scientific and technical vocabulary, and it talks about things that have the same value, the same measure or the same shape.
Iso- is mostly scientific, but some words reach daily life: gym exercises where you hold a position without moving, weather maps with lines of equal pressure, or drinks that replace what you lose when you sweat. Learning this prefix opens dozens of technical terms at once, because they all follow the same logic: "equal in something".
Combines mainly with Greek and Latin roots in scientific contexts:
Pronunciation: /ˈaɪ.soʊ/.
iso-/ˈaɪ.soʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Classic false etymology trap. "Isolate" derives from Italian "isolato" and Latin "insula" (island). It has no connection to iso- meaning equal. True iso- appears only in scientific terms: isotope, isosceles, isobar, isotherm, isometric.
A trick to remember it
Think of two sides that are exactly equal: iso- = equal. isometric, isotope.
Exercise 1 · Form the word
Exercise 2 · Pick the right one
How many equal sides does an isosceles triangle have?
The prefix iso- means "equal" or "same": isotope, isosceles, isometric, isobar, isotherm, isomer.
The prefix iso- is pronounced /ˈaɪ.soʊ/. For example, "isotope".
"tope" becomes "isotope". It is a typical example of the iso- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.