From an unused root meaning to be high or rounded; a helmet (as arched) -- helmet. Compare qowba'.
see HEBREW qowba'
H3553. koba
כּוֺבַע noun masculine helmet (√ dubious; Late Hebrew כּוֺבַע, Aramaic כּוֺבְעָא turban; compare קוֺבַע Ezekiel 23:24) — absolute ׳כ 27:10; כּוֺבָ֑ע 38:5; construct כּ֫וֺבַע (Ew§ 213, f.) 1 Samuel 17:5; Isaiah 59:17; plural כּוֺבָעִים Jeremiah 46:4; 2 Chronicles 26:14; — helmet, of bronze ׳כ עַלרֿאֹשׁוֺ נְחשֶׁת 1 Samuel 17:5; Jeremiah 46:4; Ezekiel 27:10; 38:5; 2 Chronicles 26:14; figurative of בְּראֹשׁוֺ וְכ כַּשִּׁרְיָן צְדָקָה ׳וַיִּלְבַּשׁ יְשׁוּעָה ׳י, Isaiah 59:17.