1. mentally ill or insane; suffering from a disorder of the mind
Usage: archaic or literary
2. foolish or senseless; lacking good judgment
Usage: archaic or literary

Examples

• The brainsick king made decisions that endangered his entire kingdom.
• His brainsick schemes were doomed to fail from the start.
• She dismissed his brainsick ideas as the ravings of a disturbed mind.
• The brainsick behavior of the character drove the plot of the tragedy.
• No brainsick person would attempt such a dangerous and foolish venture.