1.VerbTo be in a casual or illicit romantic relationship.
"Brad and Mary have a thing.; They’ve got a thing.; They had a thing, but it's over now."
2.VerbTo have a crush on, or a soft spot for, someone or something. .mw-parser-output .object-usage-tag{font-style:italic}.mw-parser-output .deprecated{color:var(--wikt-palette-grey-lime-8,olivedrab)}[ with for]
"Brad has a thing for Mary.; I have a thing for ghost stories."
3.VerbTo have an issue, such as a hang-up. [ with about]
"Don't ask Mary to drive you there, because she has a thing about highway driving. It sometimes gives her panic attacks.; He has a thing about not stepping on sidewalk cracks."