adjective alert; knowing; wise to. There is some confusion about whether this idiom should be construed nominally with 'a' being the article and 'wake-up' being a noun, meaning 'an alert person, a person who knows what's what', or adjectivally as defined here. The earliest evidence (from 1916) supports the noun theory, but since the 1940s it has become impossible to definitely determine the part of speech in print as it is found spelt variously as 'a wake-up', 'a wakeup', 'awake up' and 'awake-up'. The fact that the plural form 'wake-ups' is only attested by a solitary citation from 1943 suggests that it is now conceived of as an adjectival phrase however it may be spelt AUSTRALIA, 1916