-ish

CIDE DICTIONARY

-ish,  [AS. -isc; akin to G. -isch, OHG. -isc, Goth. & Dan. -isk, Gr. . Cf. -esque.].

 A suffix used to from adjectives from nouns and from adjectives. It denotes relation, resemblance, similarity, and sometimes has a diminutive force; as, selfish, boyish, brutish; whitish, somewhat white.  [1913 Webster]

-ish,  [OE. -issen, fr. F. -is, -iss- (found in the present particle, etc., of certain verbs, as finir to finish, fleurir to flourish), corresponding to L. -escere, an inchoative ending.].

 A verb ending, originally appearing in certain verbs of French origin; as, abolish, cherish, finish, furnish, garnish, impoverish.  [1913 Webster]

OXFORD DICTIONARY

-ish, suffix forming adjectives:
1 from nouns, meaning: a having the qualities or characteristics of (boyish). b of the nationality of (Danish).
2 from adjectives, meaning 'somewhat' (thickish).
3 colloq. denoting an approximate age or time of day (fortyish; six-thirtyish).

-ish, suffix (also -ise) forming verbs (vanish; advertise).

Etymology

from or after F -iss- (in extended stems of verbs in -ir) f. L -isc- incept. suffix