Meanings

to harden by kneading

thickheaded

stiff-consistency concrete

solemn promise

to make a firm resolution

firmly determined

to fortify the frontier

to harden earth into a mass

iron ingot

incarnation of selfishness

to compact

making replacements for defensive purposes in the late inning of a game

solid (an assured, a safe) vote

serious topic (of conversation)

determined

stubborn

headstrong

being faithful to one's principles

(a fortress being) impregnable

firm