-in

plural -ins

1. Used, as a modification of -ine, to form the names of a variety of types of compound; examples include proteins (globulin), carbohydrates (dextrin), dyes (alizarin) and others (vanillin).
   1. countableuncountablebiochemistryA neutral chemical compound.

      albumin, casein, chitin, pepsin, saponin

   2. countableuncountablebiochemistryAn enzyme.

      renin, pancreatin

   3. countableuncountablebiochemistryAn antibiotic.

      penicillin, streptomycin

   4. countableuncountablebiochemistryA pharmaceutical product.

      cobalamin, niacin, vitamin

plural -ins

1. Attached to a word (usually a verb) to denote a protest, demonstration or other type of gathering characterized by the activity denoted by the base word.

   At Stanford 380 students volunteered to give blood for military and civilian casualties in South Viet Nam: Ohio State held a similar “bleed-in.”

   1965 November 19, “Universities: The Spectrum on Viet Nam”, in Time, volume 86, number 21, page 67

alternative -in’

1. alternativedialectalinformalAlternative form of -ing.

1. alternativeAlternative form of -en.

   elf + -in → elfin