Ordinary is related to Basic. Basic is related to Bitter. Bitter is the opposite of Optimistic. 
Invitation is related to Offer. Offer is related to Business. Business is related to Store. 
Ordinary <--RelatedTo--> Basic <--RelatedTo--> Bitter <--Antonym--> Optimistic 
Invitation <--RelatedTo--> Offer <--RelatedTo--> Business <--RelatedTo--> Store 