Except for; unless (something occurs).

Archaic; with the exception of; excepting

1. only, merely
2 Scottish; outside
3. To the contrary
4 — used as an intensive

As an exception; all but.

With the exclusion or exception of

Other than; but, except

ETYM Formerly, onles, onlesse, onlesse that, that is, in less, in a less case. Related to On, and Less.
1. Upon any less condition than (the fact or thing stated in the sentence or clause which follows).
2. If not; supposing that not; if it be not; were it not that; except.