1. (adverb) in a way that was not expected

• out of the blue

2. (adverb) without advance planning

• accidentally
• by chance
• circumstantially

1. (adverb) without advance planning

• advisedly
• by choice
• by design
• deliberately
• designedly
• intentionally
• on purpose
• purposely

1. (adverb) in a way that was not expected

• unexpected

2. (adverb) without advance planning

• unexpected