apropos
Concise Oxford English Dictionary © 2008 Oxford University Press:
apropos /ˌaprəˈpəʊ, ˈaprəpəʊ/
▶preposition with reference to.
– phrases
apropos of nothing having no relevance to any previous discussion or situation.
apropos of nothing having no relevance to any previous discussion or situation.
– origin C17: from Fr. à propos ‘(with regard) to (this) purpose’.
'apropos' also found in these Oxford entries:

