Relating to or characteristic of an annexe or something annexed; pertaining to things joined or attached to a main structure.
From annex plus the suffix '-al' meaning relating to, from Latin 'annectere' (to bind) with Romance-language adjectival formation.
Architects use the term 'annexal structures' to describe how new buildings connect to old ones—it's a way of thinking about how different time periods literally get joined together in cities.
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