A grip or grasp; possession or understanding of something (usually used in phrases like 'get ahold of').
From 'a-' (Old English preposition meaning 'on, at') + 'hold' (grasp). Originally two words 'a hold,' it merged into one word over time and now appears mainly in informal speech.
The phrase 'get ahold of yourself' is interesting because it uses an action word (getting) with an abstract thing (control)—it shows how English lets us treat mental states as if they're physical objects we can grab, which is called 'conceptual metaphor.'
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