Capital-city names are not random. They record who founded the city, when, in what language, and often why. Learning the recurring elements turns a list of 194 words into a set of patterns, and patterns are far easier to remember.
-abad ("inhabited place", Persian)
From Persian ābād, "cultivated" or "populated place". It runs across the Persianate world: Islamabad (Pakistan) means roughly "place of Islam"; the same element appears in Hyderabad, Ahmedabad, Allahabad and Jalalabad. Ashgabat, the capital of Turkmenistan, contains a related root. When a capital or major city ends in -abad, think South and Central Asia.
-grad / -gorod ("town", Slavic)
Belgrade means "white city" (beo + grad). The element fills the Slavic world in non-capitals too: Volgograd, Kaliningrad, Novgorod, Petrograd (the wartime name of St Petersburg). If a place name ends in -grad, it is almost certainly Slavic.
San- / Santo- / São- ("saint", Iberian)
Spanish and Portuguese colonisers named settlements after the saint's day on which they were founded. Capitals: San José (Costa Rica), San Salvador ("Holy Saviour", El Salvador), Santo Domingo (Dominican Republic), São Tomé ("Saint Thomas", São Tomé and Príncipe). The pattern points to Latin America and Lusophone Africa. San Marino and San Salvador de Jujuy show it in Europe and Argentina too.
-ville and "free" names
Libreville, the capital of Gabon, means "free town" — it was founded as a settlement for freed slaves, exactly like Freetown in Sierra Leone. Monrovia (Liberia) was named for US President James Monroe and founded for the same purpose. Georgetown, Kingstown, Jamestown and Roseau show the British naming habit across the Caribbean.
"City" as the name
In Central America especially, the capital simply takes the country's name plus "City", to distinguish it from the country itself: Guatemala City, Panama City, Mexico City, Belize City (a former capital), plus Kuwait City and Vatican City elsewhere. If a country and its capital share a name, the capital is often the "City" version.
Nou- and "new" capitals
New Delhi is the obvious one. Mauritania's Nouakchott and Nouadhibou share a "nou-" element from a local language. Purpose-built modern capitals sometimes carry a grand new name: Naypyidaw translates roughly as "abode of kings" or "royal city of the sun"; Brasília is simply the feminine of "Brazil".
-town and -burg / -burgh
Germanic "burg" (fortress) gives Luxembourg ("little fortress"), Johannesburg, Hamburg, Strasbourg. Pretoria is named after the Voortrekker leader Andries Pretorius. Windhoek, the capital of Namibia, is Afrikaans/German for "windy corner".
Next time a capital is on the tip of your tongue in Guess the Capital, run through the suffixes — one of them usually fits, and it points you to the region.
Use the patterns →Meaning, not just sound
Many capital names translate to something concrete, and the meaning is a memory hook in itself. Buenos Aires is "good airs" (fair winds); Montevideo is thought to derive from "I see a mountain"; Addis Ababa is "new flower"; Ulaanbaatar is "red hero"; Tokyo is "eastern capital", paired with Kyoto, the older "capital city"; Reykjavík is "smoky bay", from the steam of its hot springs; Khartoum is said to mean "elephant's trunk", from the shape of the land where the Blue and White Nile meet.