inst. abbrev. of instant a. 2 b. 1771J. Wedgwood Let. 7 Sept. (1965) 113 Letters of the 3rd 4th and 5th inst.1954Crooks & Dawson Dict. Typewriting (ed. 6) 146 The principal commercial abbreviations beginning with this letter [sc. the letter I] are—..Inst. [etc.].