1 staunch

2 strong

1 to persevere with

2 to persist in

3 to insist on

1 to believe firmly

2 without any doubt

1 firm

2 firmly

3 hard

4 stable

1 to hold fast to

2 to stick to

1 to fortify defenses and raze the fields (idiom); to leave nothing for the invader

2 scorched earth policy

1 solid as a boulder (idiom); absolutely secure

2 rock-firm and unyielding

1 staunch and unyielding (idiom); steadfast

1 to persevere unremittingly (idiom); to keep going until the end

1 to stick to sth without change (idiom); to persevere