From an unused root meaning to accumulate; treasure -- riches, wealth.
Englishman's Concordance
1) riches, treasures Part of Speech: noun masculine A Related Word by BDB/Strong’s Number: from an unused root meaning to accumulate Same Word by TWOT Number: 1367
Brown-Driver-Briggs
[נֶ֫כֶס] noun masculineJoshua 22:8 only plural נְכָסִיםriches, treasures (probably Assyrian or Aramaic loan-word, compare Assyrian nikâsu, property, wealth, gain, DlHWB 463, Syriac wealth; on derivation from Assyrian nikâsu, cut off, hew down, behead, etc., Syriac slay, ᵑ7נְכַס, Late Hebrew נָכַסid., through meaning cattle for slaughter, compare Frä98 HptHebraica.iii (Jan.1887), 107 ff. SchwIdioticon 120f. Brockad voc.); — Joshua 22:8 (P), 2 Chronicles 1:11,12; Ecclesiastes 6:2 (all "" עשֶׁר, כָּבוֺד), Ecclesiastes 5:18 ("" עשֶׁר).
Joshua 22:8 HEB:אֲלֵיהֶ֜ם לֵאמֹ֗ר בִּנְכָסִ֨ים רַבִּ֜ים שׁ֤וּבוּ NAS: with great riches and with very KJV: with much riches unto your tents, INT: and to said riches great Return
2 Chronicles 1:11 HEB:שָׁ֠אַלְתָּ עֹ֣שֶׁר נְכָסִ֤ים וְכָבוֹד֙ וְאֵת֙ NAS: for riches, wealth or honor, KJV: riches, wealth, or honour, INT: ask riches wealth honor the life
2 Chronicles 1:12 HEB:לָ֑ךְ וְעֹ֨שֶׁר וּנְכָסִ֤ים וְכָבוֹד֙ אֶתֶּן־ NAS: you riches and wealth and honor, KJV: thee riches, and wealth, and honour, INT: have been granted riches and wealth and honor will give
Ecclesiastes 5:19 HEB:הָאֱלֹהִים֩ עֹ֨שֶׁר וּנְכָסִ֜ים וְהִשְׁלִיט֨וֹ לֶאֱכֹ֤ל NAS: riches and wealth, He has also empowered KJV: riches and wealth, and hath given him power INT: God riches and wealth empowered to eat
Ecclesiastes 6:2 HEB:הָאֱלֹהִ֡ים עֹשֶׁר֩ וּנְכָסִ֨ים וְכָב֜וֹד וְֽאֵינֶ֨נּוּ NAS: riches and wealth and honor KJV: riches, wealth, and honour, INT: God riches and wealth and honor nothing
wealth; on derivation from Assyrian nikâsu, cut off, hew down, behead, etc., Syriac 
slay, ᵑ7נְכַס, Late Hebrew נָכַסid., through meaning cattle for slaughter, compare Frä98 HptHebraica.iii (Jan.1887), 107 ff. SchwIdioticon 120f. Brockad voc.); — Joshua 22:8 (P), 2 Chronicles 1:11,12; Ecclesiastes 6:2 (all "" עשֶׁר, כָּבוֺד), Ecclesiastes 5:18 ("" עשֶׁר).