Hill. Written Knock, Cnoc, Knocka — the same Irish word, cnoc, in the spellings English gave it.
Cnoc is a hill, and the commonest hill-word in the country. It is pronounced with the c sounded in Irish, knuk, and English kept the k in spelling while dropping it in speech, which is why Knock in Mayo is 'nock'. Knock- names describe the hill itself (Knockmealdown, the hill of Maoldomhnach; Knocknarea, Cnoc na Riabh, which Joyce read as the hill of the executions) far more often than a settlement on it.
Source: P. W. Joyce, The Origin and History of Irish Names of Places (1869–1913) · Logainm ↗
Hill: it is the Irish cnoc. Cnoc is a hill, and the commonest hill-word in the country. It is pronounced with the c sounded in Irish, knuk, and English kept the k in spelling while dropping it in speech, which is why Knock in Mayo is 'nock'.
cnoc. English spellings of the same word include Knock, Cnoc, Knocka, because the names were written down by ear.