Head is the opposite of Foot. Foot can be used for Movement. Movement is related to Exercise. Exercise is a synonym of Drill. 
Client is similar to Customer. Customer is related to Service. 
Head <--Antonym--> Foot --UsedFor--> Movement <--RelatedTo--> Exercise <--Synonym--> Drill 
Client <--SimilarTo--> Customer <--RelatedTo--> Service 