'Grate' used to have two different meanings, with totally different roots. 'Grate' used to be an adjective meaning 'agreeable, thankful'. It came from the Latin 'gratus', meaning agreeable. It is no longer used, but 'grateful' stayed with us - don't ask me why. The other meaning of 'grate' is still with us and comes from the Latin 'cratus', meaning wickerwork. If you scraped a grate (latticed network) over your skin, it would hurt, hence its meaning. It just got to be pronounced differently from its original root as the language developed.

It cannot be said that they are in opposite directions. They have different meanings, yes, but they don't have opposite meanings at all ! ************************************************************************************** GRATE 1. a frame of metal bars for holding fuel when burning, as in a fireplace, furnace, or stove. 2. a framework of parallel or crossed bars, used as a partition, guard, cover, or the like; grating. 3. a fireplace. Origin: 1350–1400; Middle English < Medieval Latin : grāta : a grating, variant of crāta : wickerwork, hurdle ************************************************************************************** GRATEFUL 1. warmly or deeply appreciative of kindness or benefits received; thankful: I am grateful to you for your help. 2. expressing or actuated by gratitude: a grateful letter. 3. pleasing to the mind or senses; agreeable or welcome; refreshing: a grateful breeze. 1545–55; (obsolete) grate : pleasing (< Latin grātus ) + -ful ************************************************************************************** So, as you see, Grate has come from Medieval Latin "grāta " whereas Grateful from the Latin word grātus. they, therefore, have different roots !