English UsageGrammar guide
Plural of Tropics
Do not add another plural ending to “tropics”; distinguish singular “tropic” from plural “tropics.”
“Tropic” is singular; “tropics” is plural. In geography, “the tropics” names the region around the equator between the two tropic lines.
Key details
Confusion Familyplural-form interpretation
Rule Familynumber and lexicalized plurals
Termstropic, tropics
Variant Scope“Tropics” is already the plural form of “tropic” and commonly appears in the fixed geographic expression “the tropics.”
Further guidance
Core difference
Do not add another plural ending to “tropics”; distinguish singular “tropic” from plural “tropics.”
Fast Test
Use “a tropic” only where the singular concept is intended; use “the tropics” for the geographic region.
Usage Boundary
The familiar geographic expression is plural in form even though it can name one broad region.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Tropic — Cambridge Dictionary (opens in a new tab)Cambridge University Press · Direct dictionary evidence for singular “tropic” in the names/concept of the two boundary lines and for plural “the tropics.”
- Tropics — Cambridge Dictionary (opens in a new tab)Cambridge University Press · Direct dictionary evidence for “the tropics” as a plural expression naming the hot region around the equator.