The term 'plant firmly' can be broken down into four crossword solutions: EMBED, IMBED, ENROOT, and ENTRENCH. To EMBED something is to fix it firmly in a surrounding mass, such as when a nail is embedded in a wall. To IMBED something is to fix it firmly in a surrounding mass, but with the added connotation of making it an integral part of the mass, such as when a stone is imbedded in concrete. To enroot something is to fix it firmly in the ground, such as when a tree is planted. To ENTRENCH something is to fix it firmly in a position, such as when a military unit is entrenched in a defensive position.