How many letters does the top answer for “a period of 10 years” have?

The most common answer is decade (6 letters).

Crossword clue: a period of 10 years

3 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

decade 6 letters wn-def

a period of 10 years

decennary 9 letters wn-def

a period of 10 years

decennium 9 letters wn-def

a period of 10 years

a period of 100 years 100% similar → century

a period of five years 67% similar → quinquennium

a period of four years 67% similar → quadrennium

a space or period of four years. 50% similar → quadrennium

half a year; a period of 6 months 50% similar → semester

of or relating to or completing a period of 100 years 50% similar → centenary, centennial

of or relating to or completing a period of 200 years 50% similar → bicentenary, bicentennial

of or relating to or completing a period of 300 years 50% similar → tricentennial