Probably from sun; common, i.e. (literally) shared by all or several, or (ceremonially) profane -- common, defiled, unclean, unholy.
see GREEK sun
1. as in Greek writings from Hesiod (Works, 721) down (opposed to ἴδιος) common (i. e. belonging to several, Latincommunis): Acts 2:44; Acts 4:32; κοινῇ πίστις, Titus 1:4; σωτηρία, Jude 1:3.
2. by a usage foreign to classical Greek, common i. e. ordinary, belonging to the generality (Latinvulgaris); by the Jews opposed to ἅγιος, ἡγιασμένος, καθαρός; hence unhallowed, Latinprofanus, levitically unclean (in classical Greek βέβηλος, which see 2): Mark 7:2, 5 (where R L marginal reading ἀνίπτοις); Romans 14:14; Hebrews 10:29; Revelation 21:27 (Rec. κοινοῦν) (1 Macc. 1:47; φαγεῖν κοινά; 1 Macc. 1:62; κοινοῖ ἄνθρωποι, common people,profanum vulgus, Josephus, Antiquities 12, 2, 14; οἱ τόν κοινόν βίον προηρήμενοι, i. e. a life repugnant to the holy law, ibid. 13, 1, 1; οὐ γάρ ὡς κοινόν ἄρτον οὐδέ ὡς κονον πόμα ταῦτα (i. e. the bread and wine of the sacred supper) λαμβάνομεν, Justin Martyr, Apology 1, 66; (οἱ Χριστιανοι) τράπεζαν κοινήν παρατιθενται, ἀλλ' οὐ κοινήν, a table communis but not profanus, Ep. ad Diogn. 5 [ET], on which cf. Otto's note); κοινόν καί (R G ἤ) ἀκάθαρτον, Acts 10:14; κοινόν ἤ ἀκάθαρτον, Acts 10:28; Acts 11:8 (κοινά ἤ ἀκάθαρτα οὐκ ἐσθίομεν, Justin Martyr, dialog contra Trypho,
c. 20). (Cf. Trench, § ci.)