亚

Top horizontal stroke serving as the cap of the cross-shaped frame. Not the numeral 'one' here - a positional anchor closing the upper boundary of the symmetric figure below. Indexed under Kangxi #1 一 (yī, one) by tradition via this very stroke, used as the indexing convention rather than a content-bearing radical.

Symmetric cross-frame functioning as an abstract enclosure-pattern; the 业-like strokes are reused purely graphically here with no meaning link to 'industry'. Carries the 'second, sub-, secondary' meaning (one rank below the centre). Historically pictured a tomb floor-plan or sacred enclosure with four cornered chambers.