GNU Collaborative International Dictionary of English

Found one definition

1.       
   Lignify (lĭgˈnĭ‑fī), v. t. [imp. & p. p. Lignified (lĭgˈnĭ‑fīd); p. pr. & vb. n. Lignifying (lĭgˈnĭ‑fīˌĭng).] [L. lignum wood + -fy: cf. F. lignifier.] (Bot.) To convert into wood or into a ligneous substance.
   
   [1913 Webster]