Definition of thumbsuck noun from the Oxford Advanced Learner's Dictionary

 

thumbsuck

 noun
noun
BrE BrE//ˈθʌmsʌk//
 
; NAmE NAmE//ˈθʌmsʌk//
 
[countable, usually singular, uncountable](South African English, informal, often disapproving)
 
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a guess or estimate Their sales projections are a total thumbsuck.