Formal:
* Instead: "Instead of going to the party, I stayed home."
* In place of: "The company offered a bonus in place of a raise."
* In the place of: "The substitute teacher taught in the place of the regular teacher."
Informal:
* Instead of: This is the most common informal synonym.
* As a replacement for: "They used a chair as a replacement for a stool."
Other options:
* Substitute: "The doctor suggested a substitute medicine."
* Replacement: "They hired a replacement for the employee who quit."
* Stead: "He stayed in his room, in stead of going out."
Example:
"In lieu of flowers, donations may be made to the charity."
In this context, "instead of" would be the most appropriate synonym: "Instead of flowers, donations may be made to the charity."