firmament

n the firmament [sing] (arch 古) the sky 天空; 苍天.

fire-water, firearm, fireball, firebrand, firecracker, firedamp (also damp), firedog, firefly, firelight, fireman, firemen, fireplace, fireproof, fireside, firewood, firework, firing, firing-line, firing-squad, firm, firmly, firmness, first, first aid, first and foremost, first balcony, first base, first class, first cousin, first degree, first finger, first floor, first gear, first lady, first name, first night, first of all, first offender, first officer, first or last,