an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator; "all points on the same meridian have the same longitude"
the occurrence of incoming water (between a low tide and the following high tide); "a tide in the affairs of men which, taken at the flood, leads on to fortune" -Shakespeare
(philosophy) a philosophical theory holding that all events are inevitable consequences of antecedent sufficient causes; often understood as denying the possibility of free will