Words

Arabic
ṯuˁāl-, ṯaˁlab- - fox (BK 1 225, Lane 237, 338)
Arabic
ṯbr - to restrain; to curse; to destroy; to perish (BK 1 217, Lane 330)
Arabic
ṯaγr- - gap, opening, breach; a frontier-way of access to a country; the part of a country from which the invasion of the enemy is feared (Lane 338)
Arabic
ṯkl - to lose (child), become bereft (Lane 345, BK 1 231)
Arabic
ṯuknat- - pearl necklace; dyed wool collar that hangs as an ornament on the camel's neck (BK 1 231)

presumably related with assimilation of *m > n after the velar. As for the semantic shift, see SED I, No. 15

Arabic
ṯallat-, ṯilal-, ṯilāl- - flock of sheep or goats (BK 1 232, Lane 346)
Arabic
ṯalāṯ- - three (Lane 347)
Arabic
ṯulāṯāˀ - Tuesday (Lane 348)
Arabic
ṯalǯ- - snow (Lane 350)
Arabic
ṯūm- - garlic (Lane 365)