Old English ilca "same" (n. and adj.), from Proto-Germanic *ij-lik, in which the first element is from the PIE demonstrative particle *i- (see yon) and the second is that in Old English -lic "form" (see like). Of similar formation are which and such. Phrase of that ilk implies coincidence of name and estate, as in Lundie of Lundie; applied usually to families, so by c.1790 it began to be used with meaning "family," then broadening to "type, sort."