From an unused root meaning to encircle; a capital of a column -- chapiter.
Englishman's Concordance
1) plated capital (of pillar) Part of Speech: noun feminine A Related Word by BDB/Strong’s Number: from an unused root meaning to encircle Same Word by TWOT Number: 1951c
Brown-Driver-Briggs
צֶ֫פֶתnoun feminine apparently plated capital of pillar2Chronicles 3:15.
צפח (√ of following; compare Arabic II. make wide, broad; anything broad (stone, plank, sheathing, plating), Syriac plating; also Ethiopic spread out, extend; Sabean (Lihyanian) הצפחת, אצפחתplatform, DHMEpigr. Denkm. 84. 86; but (transposed) Arabic , wide bowl, compare Frä63).
2 Chronicles 3:15 HEB:וְחָמֵ֖שׁ אֹ֑רֶךְ וְהַצֶּ֥פֶת אֲשֶׁר־ עַל־ NAS: high, and the capital on the top KJV: high, and the chapiter that [was] on the top INT: of each five high and the capital after on