Church (or coill, a wood). Written Kill, Kil, Keel — the same Irish word, cill, in the spellings English gave it.
Cill is a church (from Latin cella, a monk's cell) and a Kil- name almost always marks an early Christian foundation, usually with a saint's name attached: Kilbride is Brigid's church, Kilkenny is Cainneach's. The trap is coill, a wood, which anglicises to the same Kil- or Kyle-, so that Kilmore may be the big church or the big wood. Joyce reckoned the church reading right in the great majority of cases, and the local saint's day usually settles it.
Source: P. W. Joyce, The Origin and History of Irish Names of Places (1869–1913) · Logainm ↗
Church (or coill, a wood): it is the Irish cill. Cill is a church (from Latin cella, a monk's cell) and a Kil- name almost always marks an early Christian foundation, usually with a saint's name attached: Kilbride is Brigid's church, Kilkenny is Cainneach's. The trap is coill, a wood, which anglicises to the same Kil- or Kyle-, so that Kilmore may be the big church or the big wood.
cill. English spellings of the same word include Kill, Kil, Keel, because the names were written down by ear.
Kilkenny (Cill Chainnigh), Kildare (Cill Dara), Killarney (Cill Airne), Enniskillen (Inis Ceithleann), Kilrush (Cill Rois), Killaloe (Cill Dalua).