Keep is a synonym of Sustain. Sustain is a synonym of Maintain. 
Chocolate is related to Sweet. Sweet is related to Desert. you are likely to find Shadow in/at/on Desert. Shadow is related to Ghost. 
Keep <--Synonym--> Sustain <--Synonym--> Maintain 
Chocolate <--RelatedTo--> Sweet <--RelatedTo--> Desert <--AtLocation-- Shadow <--RelatedTo--> Ghost 