1) a musical instrument 1a) probably the lyre or zither
Full Brown-Driver-Briggs lexicon entry
קיתרס Kt, קַתְרֹס Qr, noun [masculine]lyre, zither (also ᵑ7; loan-word from Greek κίθαρις Kraussi. 193: ii. 573); — Dan 3:5; Dan 3:7; Dan 3:10; Dan 3:15 Kmp קִיתָרִם.