Wiktionary
propeller head
alt. 1 The hub of a propeller 2 The central part of a propeller, into which the blades fit 3 (context informal English) A person deeply absorbed in an academic field or technical interest, especially to the exclusion of social activities. n. 1 The hub of a propeller 2 The central part of a propeller, into which the blades fit 3 (context informal English) A person deeply absorbed in an academic field or technical interest, especially to the exclusion of social activities.