Excuse is a synonym of Relieve. Relieve is a type of Rid. Rid is a synonym of Free. 
Pole is related to Telescope. Lens can be used for Telescope. Lens is related to Photography. Camera can be used for Photography. 
Excuse <--Synonym--> Relieve --IsA--> Rid <--Synonym--> Free 
Pole <--RelatedTo--> Telescope <--UsedFor-- Lens <--RelatedTo--> Photography <--UsedFor-- Camera 