Meaningful is similar to Significant. Significant is related to Importance. Importance is related to Value. Value is related to Heat. 
Plant is the opposite of Harvest. Machine can be used for Harvest. Machine is related to Mechanical. 
Meaningful <--SimilarTo--> Significant <--RelatedTo--> Importance <--RelatedTo--> Value <--RelatedTo--> Heat 
Plant <--Antonym--> Harvest <--UsedFor-- Machine <--RelatedTo--> Mechanical 