NieR

Words are randomly obtained from shades. The more powerful the shade, the more powerful the word. I would be surprised if you do not have this achievement naturally by the end of your second playthrough without farming for it at all, maybe even earlier.

You do not need the tier 1 +weapon dmg word to get the next higher +weapon dmg word. You will get ones all over the place and most certainly never pick up certain ones, but it is not important for reasons I will mention below.

Different and stronger types of shades will take the place of weaker shades as you progress the story and especially when you begin to collect key fragments to the shadowlord's castle. So, between each key fragment and major event in the story, if you really want to farm words fast, check each area for different looking shades because every type has specific words that only that type drops. You will fight plenty of the shades that give you the highest +atk dmg% and +magic dmg words in the end of the game, so you'll pretty much assuredly snag those, but a lot of the lower level words you are likely to miss. I have done all 4 endings with about 45 hours played and certainly 10s of thousands of shades killed and I think I have around 67 or 70% of the words. Most of the ones I missed I think were from the first half of the game against the very weakest shades that you never see again since I was going for lightspeed fighter.

Update: if you want to go get a ton of words in a hurry, you can enter a dream sequence in which you fight waves of all manner of shades starting from the very weakest ones in the game. Just going through it once (takes about 3 or 4 minutes) I think I picked up 5 words at least, and going through it again I kept on getting more. Here is the quest:
Quest: The Magical Stone
-You get this quest rather late in the game- you either have to have most of the key fragments or have done a lot of other quests to trigger it to be available, but I wasnt able to pick it up until well after I had completed the 30 quests achievement. It starts from an npc in the Forest of Myth. Devola in the village tavern will also give you a notification to go meet her for the quest if it's available for you. When you are sent to the top of the Lost Temple to look for the stone, as you get to the roof area with the crumbled rooms outside look to the right for a box you can pull around the corner and move it so you can jump up and get into another room where you can continue to make some pretty tricky jumps to get to the areas you can see on the east side of the map minimap.) Once you return to the lady in the Forest of Myth choose to get your fortune told. You will enter a "dream" area where you fight many shades, starting out from the very weakest to progressively stronger ones. Among these are shades that drop rusty kitchen knives. Also, behind the shelves in the building is the iron pipe weapon. You can have her tell your fortune as many times as you want to keep going back into this area and battle more if you have reason to.