纤芯

纤芯	xiān xīn	core (of a fiber)
纤	qiàn	boatman's tow-rope
纤	xiān	fine / delicate / minute
芯	xīn	(bound form) the pith of the rush plant (used as a lampwick)
芯	xìn	used in 芯子 / Taiwan pr. [xin1]