Entry 1 sense Webster, 1913 Renning /(r?n"n?ng)/ · Ren·ning · IPA /ˈɹɛnɪŋ/ 01 n. See 2d Rennet. 1. See 2d Rennet.[Obs.] See: Rennet “Asses' milk is holden for to be thickest, and therefore they use it instead of renning, to turn milk.” — Holland.