This paper gives explanation of the meaning extension of the symbolic adverbs by introducing `inferential feature`. In spite of all criticism by the prototypical semanticist, the notion of feature is still of some use for semantics. According as the adverb `ttak` symbolizing sounds and situations extends its meaning, it mainly gains the mimetic or modal meaning instead of losing the onomatopoeic characteristics. The inferential features involved in the meaning extension of ttak are momentariness, exactness, adjacency, and completeness.