adjective
awake, alert
A2
wach means awake or alert. It's a gradable adjective (comparative: 'wacher', superlative: 'am wachsten') used predicatively or attributively. Antonyms include 'müde' and 'schlafend'. Not a participle; regular inflection. Neutral register, common to describe attention or sleep state. Used in spoken and written German.
Examples
Er ist sehr wach und aufmerksam im Unterricht.
He is very alert and attentive in class.
Der Patient war wach, obwohl die Operation bereits begonnen hatte.
The patient was awake, although the operation had already begun.
Ich bin schon seit fünf Uhr wach.
I've been awake since five o'clock.
Details
Mnemonics
Imagine big open eyes staring at a clock early in the morning.
Think 'watch' — when you're awake you watch things.
Notes
Can mean simply 'not asleep' or 'mentally alert'.