Solutions So as to become invisible has 7 entries with similar clues

• 3-letter words
• inkInvisible ...... (medium for a secret message)
• 4-letter words
• auraAn invisible or subtle emanation
• 7-letter words
• relapseagain become invalid, or again become invalid
• 13-letter words
• birthday-suitInvisible attire/outfit
• imperceptibleInvisible
• indiscernibleInvisible
• 15-letter words
• out-of-thin-airForm a state of being invisible or nonexistent