Pipe is a synonym of Vertical. Vertical is related to Steep. Steep is the opposite of Cheap. Cheap is the opposite of Buy. 
Works is a synonym of Plant. Plant is related to Grass. you are likely to find Stick in/at/on Grass. 
Pipe <--Synonym--> Vertical <--RelatedTo--> Steep <--Antonym--> Cheap <--Antonym--> Buy 
Works <--Synonym--> Plant <--RelatedTo--> Grass <--AtLocation-- Stick 