A person who foosters; someone who wastes time with aimless tinkering or fidgeting.
From 'fooster' (dialectal) with the agent suffix '-er' added, creating a person who characteristically engages in the action.
In English, we can pile on suffixes almost endlessly—'foost' becomes 'fooster' (the action) which becomes 'foosterer' (the person)—this layering shows how language lets us express increasingly specific ideas about human behavior.
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