Does four-square mean completely?

[Nenad11]

English Language Tests, Intermediate level

ESL/EFL Test #352 "English Slang Idioms (73)", question 10

"I think that you will do a great job as County Treasurer. You have my vote. I am .........-square behind you," her friend told her.

(a) three
(b) tee
(c) four
(d) frame

English Language Tests, Intermediate level

ESL/EFL Test #352 "English Slang Idioms (73)", answer 10

"I think that you will do a great job as County Treasurer. You have my vote. I am four-square behind you," her friend told her.

Correct answer: (c) four

Your answer was: incorrect
"I think that you will do a great job as County Treasurer. You have my vote. I am frame-square behind you," her friend told her.
_________________________

Does four-square mean completely,with one's whole being?

[Linda]

It means to be determined or certain about something.
_________________
One Way of Learning English Grammar
Learn English with Linda Arlia

[Puppet]

Hi,

I've got mixed up. If you allow me to ask;

Does 'four-square' hold the meaning of ''i'm in all the way''? like she's her rock.

Or it means being ''positive'' that she will take the chair?