熔く[toku] to dissolve (paint)
熔ける[tokeru] to melt
熔岩[yougan] lava
熔鉱炉[youkouro] smelting furnace
熔接[yousetsu] weld

熔融[youyuu] melting
熔解[youkai] melting
熔銑[yousen] molten iron
炉心熔融[roshinyouyuu] core meltdown
熔滓[youshi] slag

偏芯[henshin] eccentricity (in mechanics, electronics, etc.)
燈芯[toushin] (lamp) wick
帯芯[obishin] thick obi sash
摘芯[tekishin] thinning (buds and branches)
芯地[shinji] padding

替え芯[kaeshin] spare lead
鉛筆の芯[enpitsunoshin] lead of a pencil
硬の芯[kounoshin] hard pencil lead
林檎の芯[ringonoshin] core of an apple