Monomania is a noun that refers to an obsession with one particular thing.

We have the Greeks to thank for our word of the day. The prefix M-O-N-O means ‘single’ or ‘alone.’ And the Greek word mania refers to an excessive enthusiasm or obsession. Together they get monomania, an enthusiastic preoccupation with one particular thing.

Andrew’s fascination with potatoes became pretty weird after a while. His monomania reached the point where potatoes were all he wanted to eat — no matter how much damage this did to his digestive system.