How many letters does the top answer for “the cardinal number that is the sum of six and one” have?

The most common answer is heptad (6 letters).

Crossword clue: the cardinal number that is the sum of six and one

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

heptad 6 letters wn-def

the cardinal number that is the sum of six and one

septenary 9 letters wn-def

the cardinal number that is the sum of six and one

seven 5 letters wn-def

the cardinal number that is the sum of six and one

vii 3 letters wn-def

the cardinal number that is the sum of six and one

the cardinal number that is the sum of one and one and one 80% similar → iii, tercet, ternary

the cardinal number that is the sum of eight and one 67% similar → ennead, nine, niner

the cardinal number that is the sum of eleven and one 67% similar → dozen, twelve, xii

the cardinal number that is the sum of five and one 67% similar → hexad, sextuplet, six

the cardinal number that is the sum of four and one 67% similar → cinque, five, pentad