I came across the sentence "They have set watch to kill you." but I wonder if the word "watch" need to change to "watches" or "a watch". Isn't noun plural form like "es" always necessary?
Then he pulled him out of the river, and said to him, as he got upon the bank, 'Your brothers have set watch to kill you, if they find you in the kingdom.' So he dressed himself as a poor man, and came secretly to the king's court, and was scarcely within the doors when the horse began to eat, and the bird to sing, and princess left off weeping.
The Golden Bird by Brothers Grimm