How many letters does the top answer for “home of house of the unions” have?

The most common answer is moscow (6 letters).

Crossword clue: home of house of the unions

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

moscow 6 letters wd-fact-v3

a city of central European Russia; formerly capital of both the Soviet Union and Soviet Russia; since 1991 the capital o

tverskoydistrict 16 letters wd-fact-v3

home of abbasi house 50% similar → kashancounty

home of apsley house 50% similar → cityofwestminster

home of banqueting house 50% similar → cityofwestminster

home of blue house 50% similar → jongnodistrict

home of borujerdi house 50% similar → kashancounty

home of burghley house 50% similar → barnack, stmartinswithout

home of burlington house 50% similar → cityofwestminster

home of chinese house 50% similar → brandenburgervorstadt