The Collaborative International Dictionary of English v.0.48:
-ist \-ist\ ([i^]sh"[-u]*[i^]st). [Gr. ?: cf. F. -iste.] A noun suffix denoting an agent, or doer, one who practices, a believer in; as, theorist, one who theorizes; socialist, one who holds to socialism; sensualist, one given to sensuality. [1913 Webster]The Collaborative International Dictionary of English v.0.48:
Is't \Is't\ A contraction of is it. [1913 Webster]