Relating to or of the nature of a dome; shaped like or characteristic of a dome; pertaining to dome architecture.
From dome + -ical (suffix variant of -ic, meaning 'relating to'). The -ical form is a more formal variant that emphasizes the architectural meaning.
Domical is the fancy version of 'dome-shaped'—you'd use it in architecture journals, while domic appears in more general contexts, but both are quite rare in modern English.
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