estuary
Concise Oxford English Dictionary © 2008 Oxford University Press:
estuary /ˈɛstjʊ(ə)ri/
▶noun (pl. estuaries) the tidal mouth of a large river.
– derivatives
estuarial adjective,
estuarine /-rʌɪn/ adjective.
estuarial adjective,
estuarine /-rʌɪn/ adjective.
– origin C16: from L. aestuarium ‘tidal part of a shore’, from aestus ‘tide’.
'estuary' also found in these Oxford entries:

